List of Kamen Rider Build characters

Sento Kiryū

Sento Kiryū (桐生 戦兎, Kiryū Sento) is a young genius, who, despite his narcissistic tendencies, is always willing to trust his comrades and puts the safety of others above himself. Though level-headed and compassionate, Sento is egotistical with a dangerous temper when provoked by his enemies.

Prior to the start of the series, he was found by Sōichi Isurugi in an alley, missing all of his memories except for one where he was being experimented on by Night Rogue. Sōichi gives Sento his name and convinced the youth to help him fight the Faust organization and its Smash creations in the hopes of regaining his memories. But Sento's search while helping Ryūga clear his name leads to a series of revelations that include an Evolto-possessed Sōichi masterminding the events that ruined both his and Ryūga's lives, followed by a defeated Gentoku revealing Sento's true identity.

Sento was actually Faust's founder Takumi Katsuragi, whose memories were lost after a failed assassination attempt on Evolto. After being knocked unconscious by Evolto, his face was swapped with the recently murdered musician's Tarō Satō (佐藤 太郎, Satō Tarō) to be experimented on by Gentoku as part of Evolto's plan to manipulate Sento to complete Takumi's Rider Systems from development hell to be utilized in the civil war he eventually causes. Despite multiple twist of events, Sento's faith in others allows him to join forces with Kazumi and Gentoku to fight against Evolto. After a failed suicide attack to kill Evolto, which results in him being temporarily possessed, Katsuragi re-emerges and tries to take matters into his own hands. Eventually, both Sento and Katsuragi came into terms with each others, allowing the former to regain control of his body while the latter acted as his spiritual adviser.

Following Evolto's permanent destruction, Sento learned he caused the Pandora Box to erase all traces of Evolto from his Earth which he later realized was assimilated into the "Prime" Kamen Rider universe with the Skywall Disaster and the deaths that followed all averted. This made Sento an inter-dimensional aberration as he is seen as a complete stranger or mistaken for Tarō Satō, who had also been revived and still with his music band, by the reality's versions of his friends before finding his own reality's Ryūga, who was also in the same situation, as the two decide to start their lives anew. It is later revealed that many of the previous episodes' opening recaps are actually memoirs written by Sento which he intends to use as the basis of a television series he and Ryūga are collaborating on, subtly breaking the fourth wall.

Sento is able to transform into Kamen Rider Build by using the Build Driver (ビルドドライバー, Birudo Doraibā) in conjunction with the Fullbottles (フルボトル, Furubotoru), which contain a liquefied element created by the refinement of Nebula Gas. As Build, he initially fought Faust and the Smash in the hopes of regaining his lost memories, before learning his true identity and resolving to stop the abuse of his technology. By himself, Sento's initial Hazard Level is 3, having maintained it for a year. The continuous use of the Hazard Trigger and Pandora Panel (later Genius Fullbottle) allows it to rise rapidly towards 7, allowing him to transform the Rabbit Fullbottle into a golden state.

In order to access each of his forms, Build must combine two Fullbottles, one organic (based on an animal or person) and one inorganic (based on an object), in the Build Driver to transform. Certain combinations allow him to assume either strong compatibility forms called a Best Match (ベストマッチ, Besuto Matchi), which can perform the Vortex Finish (ボルテックフィニッシュ, Borutekku Finisshu) finishing move, or weaker random forms called a Trial Form (トライアルフォーム, Toraiaru Fōmu), which can perform the Vortex Attack (ボルテックアタック, Borutekku Atakku) finishing move. The originators of the Best Match forms are inspired from Misora Isurugi's childhood drawings, according to Sōichi's past memories, which would soon being used by Evolto, through directly both Shinobu and Takumi as the samples for the bottle-based Kamen Rider Systems.

• His default Best Match is RabbitTank Form (ラビットタンクフォーム, Rabitto Tanku Fōmu), also known as the "Moonsault of Steel" (鋼のムーンサルト, Hagane no Mūnsaruto). This form is achieved by using the Rabbit (ラビット, Rabitto) Fullbottle, which gives him superhuman reflexes along with spring-like Rabbit Foot Shoes (ラビットフットシューズ, Rabitto Futto Shūzu) on his left leg, and the Tank (タンク, Tanku) Fullbottle that provides Build with the tread-like Tank Roller Shoes (タンクローラーシューズ, Tanku Rōrā Shūzu) on his right leg for enhanced kicking. The Rabbit and Tank Fullbottles are later revealed to be the "True Best Match", which is the reason why these Fullbottles are mainly used as Build's default Best Match form and for the creation samples of its related upgrade forms. Build later uses the beverage can-like RabbitTank Sparkling (ラビットタンクスパークリング, Rabitto Tanku Supākuringu) to assume an upgraded version of his default form called RabbitTank Sparkling Form (ラビットタンクスパークリングフォーム, Rabitto Tanku Supākuringu Fōmu), also known as the "Bubbling and Bursting" (シュワッと弾ける, Shuwatto Hajikeru), which allows him to use all of his Best Match weapons. This form first appears in the Kamen Rider Heisei Generations Final movie.
• GorillaMond Form (ゴリラモンドフォーム, Goriramondo Fōmu), also known as the "Shining Destroyer" (輝きのデストロイヤー, Kagayaki no Desutoroiyā), is a Best Match that uses the Gorilla (ゴリラ, Gorira) Fullbottle, which gives Build superhuman strength and the Muscle Glove (マッスルグローブ, Massuru Gurōbu) on his right arm, and the Diamond (ダイヤモンド, Daiyamondo) for increased durability and BLD Prism Glove (BLDプリズムグローブ, BLD Purizumu Gurōbu) on his left arm. Sento initially used this form as Takumi in episode 44 of Kamen Rider Ex-Aid and its film Kamen Rider Ex-Aid the Movie: True Ending before the bottles were emptied out by Evolto's deception, only for Sento to refill them back with Misora's help.
• HawkGatling Form (ホークガトリングフォーム, Hōku Gatoringu Fōmu), also known as the "Rampage of the Skies" (天空の暴れん坊, Tenkū no Abarenbō), is a Best Match that uses the Taka (タカ, Hawk) Fullbottle, which provides Build with the airfoil-like Solstall Wings (ソレスタルウィング, Soresutaru Wingu), and the Gatling (ガトリング, Gatoringu) Fullbottle, which enhances Build's accuracy. In this form or any Trial Match using either Fullbottle, Build is armed with the Hawk Gatlinger (ホークガトリンガー, Hōku Gatoringā) submachine gun that he uses for his Full Bullet (フルバレット, Furu Baretto) finishing move.
• NinninComic Form (ニンニンコミックフォーム, Ninnin Komikku Fōmu), also known as the "Sneaky Entertainer" (忍びのエンターテイナー, Shinobi no Entāteinā), is a Best Match that uses the Ninjya (ニンジャ, Ninja) Fullbottle, equipping Build with the sash-like Onmitsu Scarf (オンミツスカーフ, Onmitsu Sukāfu) on his back for enhanced agility, and the Comic (コミック, Komikku) Fullbottle, which enables Build to project illusory images. In this form or any Trial Match using either Fullbottle, Build is armed with the 4Koma Ninpoutou (4コマ忍法刀, Yon Koma Ninpōtō, Four-frame Ninja Sword) katana, which allows him to perform one of two finishing moves: Fire Jutsu (火遁の術, Katon no Jutsu, Art of Fire Releasing) or Wind Jutsu (風遁の術, Fūton no Jutsu, Art of Wind Releasing). The 4Koma Ninpoutou can also be used to initiate one of two special attacks: Clone Jutsu (分身の術, Bunshin no Jutsu, Art of Cloning) or Stealth Jutsu (隠れ身の術, Kakuremi no Jutsu, Art of Camouflage).
• RocketPanda Form (ロケットパンダフォーム, Roketto Panda Fōmu), also known as the "Flying Monotone" (ぶっ飛びモノトーン, Buttobi Monotōn), is a Best Match that uses the Panda (パンダ) Fullbottle, equipping equips Build with the Giant Scratcher (ジャイアントスクラッチャー, Jaianto Sukuratchā) claw on his right arm, and the Rocket (ロケット, Roketto) Fullbottle, which equips Build with the missile-like Space Ride Arm (スペースライドアーム, Supēsu Raido Āmu) on his left arm for projectile launching.
• FireHedgehog Form (ファイヤーヘッジホッグフォーム, Faiyā Hejjihoggu Fōmu), also known as the "Rescue Kenzan" (レスキュー剣山, Resukyū Kenzan), is a Best Match that uses the Harinezumi (ハリネズミ, Hedgehog) Fullbottle, equipping Build with the spiky Spine Knuckle (スパインナックル, Supain Nakkuru) on his right arm, and the Shoubousha (消防車, Shōbōsha, Fire engine) Fullbottle, which arms build with the hose-like Multi Deluge Gun (マルチデリュージガン, Maruchi Deryūji Gan) on his left arm for either shooting fire or spraying water.
• LionCleaner Form (ライオンクリーナーフォーム, Raion Kurīnā Fōmu), also known as the "Maned Cyclone" (たてがみサイクロン, Tategami Saikuron), is a Best Match that uses the Lion (ライオン, Raion), which arms Build with the wrist guard-like Gold Lio Gauntlet (ゴルドライオガントレット, Gorudo Raio Gantoretto) on his right arm, and the Soujiki (掃除機, Sōjiki, Vacuum cleaner) Fullbottle which equips Build with both the hoover-like Long Range Cleaner (ロングレンジクリーナー, Rongu Renji Kurīnā) on his left arm which vacuums attacks that are stored in the canister-like Trash Converter (トラッシュコンバーター, Torasshu Konbātā) on his left shoulder. Outside its compatibility with the Build Driver, the Lion Fullbottle can also be loaded into the Build Phone (ビルドフォン, Birudo Fon) for it to transform into a motorcycle known as the Machine Builder (マシンビルダー, Mashin Birudā).
• KeyDragon Form (キードラゴンフォーム, Kī Doragon Fōmu), also known as the "Sealed Fantasia" (封印のファンタジスタ, Fūin no Fantajisuta), is a Best Match uses the Dragon (ドラゴン, Doragon), which arms Build with Drago Rush Arm (ドラゴラッシュアーム, Dorago Rasshu Āmu)and Fang of Raid (ファングオブレイド, Fangu Obu Reido) spike projections, and the Lock (ロック, Rokku) Fullbottle that equips Build with the battering ram-like Bind Master Key (バインドマスターキー, Baindo Masutā Kī) and BLD Security Shoulder (BLDセキュリティショルダー, Bī Eru Dī Sekyuriti Shorudā) on his left arm, he is also able to use the Beat Closer, thanks to the Dragon Fullbottle. The form is occasional used due to the strain the Dragon Fullbottle places on Sento's body before it was given to Ryūga.
• KaizokuRessya Form (海賊レッシャーフォーム, Kaizoku Resshā Fōmu, PirateTrain Form), also known as the "Punctual Rebel" (定刻の反逆者, Teikoku no Hangyakusha), is a Best Match that uses the Kaizoku (海賊, Pirate) Fullbottle, which arms Build with Multi Sail Mantle (マルチセイルマント, Maruchi Seiru Manto) on his right shoulder for wind-power conversion, and the Densya (電車, Densha, Train) Fullbottle that equips Build with the wrist guard-like Train Gauntlet (トレインガントレット, Torein Gantoretto) on his left arm for increased speed. In this form or any Trial Match using either Fullbottle, Build is uses the bladed bow-like Kaizoku Hassyar (カイゾクハッシャー, Kaizoku Hasshā), which allows him to perform the Kaizoku Densya (海賊電車, Kaizoku Densha) finishing move. The Kaizoku Hassyar can also be used to initiate one of three special attacks: Kakueki Densya (各駅電車, Kakueki Densha, All Station Train), Kyukou Densya (急行電車, Kyūkō Densha, Express Train), or Kaisoku Densya (快速電車, Kaisoku Densha, Rapid-Service Train).
• OctopusLight Form (オクトパスライトフォーム, Okutopasu Raito Fōmu), also known as the "Lightning Technician" (稲妻テクニシャン, Inazuma Tekunishan), is a Best Match that is accessed via the Octopus (オクトパス, Okutopasu) Fullbottle, which gives Build with the tentacle-like Twist Lash Arm (ツイストラッシュアーム, Tsuisuto Rasshu Āmu) on his right shoulder, and the Light (ライト, Raito) Fullbottle which equips Build with both the fuse-like Shade Breaker (シェードブレイカー, Shēdo Bureikā) and beacon-like BLD Light Bulb Shoulder (BLDライトバルブショルダー, BLD Raito Barubu Shorudā) on his left arm to emit bright flashes.
• PhoenixRobo Form (フェニックスロボフォーム, Fenikkusu Robo Fōmu), also known as the "Immortal Weapon" (不死身の兵器, Fujimi no Heiki), is a Best Match that was introduced in Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider. The Best Match utilizes the Phoenix (フェニックス, Fenikkusu) Fullbottle, which arms Build Flame Reviber (フレイムリヴァイバー, Fureimu Rivaibā) gauntlet and Empirial Wings (エンパイリアルウィング, Enpairiaru Uingu), and the Robot (ロボット, Robotto) Fullbottle that equips Build with the mechanical arm Demolition One (デモリションワン, Demorishon Wan) for dismantling and crushing targets.
• SmaphoWolf Form (スマホウルフフォーム, Sumaho Urufu Fōmu), also known as the "Connected Lone Wolf" (つながる一匹狼, Tsunagaru Ippiki Ōkami), is a Best Match that was among the forms Sento acquired while as Takumi. The Best Match is accessed via the Wolf (ウルフ, Urufu) Fullbottle, arming Build with the Wolfatal Claw (ウルフェイタルクロー, Urufeitaru Kurō) and animal instinct, and the Smapho (スマホ, Sumaho, Smartphone) Fullbottle which equips Build with the buckler-like Build Pad Shield (ビルドパッドシールド, Birudo Paddo Shīrudo) on his left arm for either defending capabilities or selecting a recommended attack enhancement. Although the Build Pad Shield cracks upon sustaining a strong attack, it can repair itself. Befitting its identical appearance to the Build Phone, the Build Pad Shield can also function in the same manner, with the exception of Bike Mode.
• RoseCopter Form (ローズコプターフォーム, Rōzu Koputā Fōmu), also known as the "Passionate Fan" (情熱の扇風機, Jōnetsu no Senpūki) is a Best Match that is accessed via the Rose (ローズ, Rōzu) Fullbottle, allowing allows Build to manipulate vines or fire thorn projections with Ibalash Arm (イバラッシュアーム, Ibarasshu Āmu), and the Helicopter (ヘリコプター, Herikoputā) Fullbottle that equips Build with the Batrotor Blade (バトローターブレード, Batorōtā Burēdo) helicopter rotor for flight or removable weapon.
• ToraUFO Form (トラユーフォーフォーム, Tora Yūfō Fōmu), also known as the "Unidentified Jungle Hunter" (未確認ジャングルハンター, Mikakunin Janguru Hantā), is a Best Match that is accessed via Tora (トラ, Tiger) Fullbottle, increasing Build's speed while arming him with the BLD Tora Fight Glove (BLDトラファイトグローブ, Bī Eru Dī Tora Faito Gurōbu), and the UFO (UFO, Yūfō) Fullbottle which allows allows Build to conjure a UFO projection to ride on.
• KujiraJet Form (クジラジェットフォーム, Kujira Jetto Fōmu), also known as the "Sky-Flying Big Wave" (天駆けるビッグウェーブ, Amakakeru Biggu Wēbu), is a Best Match that is accessed via the Kujira (クジラ, Whale) Fullbottle, arming Build with the BLD Spout Glove (BLDスパウトグローブ, Bī Eru Dī Supauto Gurōbu) to manipulate water currents, and the Jet (ジェット, Jetto) Fullbottle which enables Build ability to do skywalk while creating mini-jets to attack.
• KirinCyclone Form (キリンサイクロンフォーム, Kirin Saikuron Fōmu), also known as the "Towering Storm-Caller" (嵐を呼ぶ巨塔, Arashi o Yobu Kyotō), is a Best Match that is accessed via the Kirin (キリン, Giraffe) Fullbottle, equipping Build with a horn-like arm to create giraffe's neck-energy punches, and the Senpuki (扇風機, Senpūki, Fan) Fullbottle that enables Build to create tornados.
• TurtleWatch Form (タートルウォッチフォーム, Tātoru Wotchi Fōmu), also known as the "Armored Time Hopper" (時を駆ける甲冑, Toki o Kakeru Katchū), is a Best Match that is accessed via the Turtle (タートル, Tātoru) Fullbottle and the Watch (ウォッチ, Wotchi) Fullbottle. This form first appears in Kamen Rider Build Episode 21 off-screen.

Build's main weapon is the Drill Crusher (ドリルクラッシャー, Doriru Kurasshā), which has two modes: Blade and Gun. By inserting a Fullbottle into a slot on this weapon's back, it can activate a Vortex Break (ボルテックブレイク, Borutekku Bureiku) finishing move. After defeating a Smash, Build can extract its element liquid into a powerless version of a Fullbottle known as an Empty Bottle (エンプティボトル, Enputi Botoru) to be purified into a new Fullbottle to utilize its abilities to either access one of his forms or charge one of his weapons. Even without the Build Driver, Sento (or anyone else) is able to channel a Fullbottle's power simply by activating it.

Sento later acquires an item called the Hazard Trigger (ハザードトリガー, Hazādo Torigā), which he created as Takumi before it fell into Sōichi's hands, to transform into a black-colored version of Build called Hazard Form (ハザードフォーム, Hazādo Fōmu) whose upgraded Super Best Match (スーパーベストマッチ, Sūpā Besuto Matchi) forms are stronger than RabbitTank Sparkling Form and equal to Sclash Driver-using Kamen Riders. Unfortunately, the Hazard Trigger induces a berserker side-effect, causing Sento to hesitate using it as he and Nariaki Utsumi add a self-destruct mechanism as a drastic measure. However, after Misora awakens her full ability of purifying the Hazard Levels of Nebula Gas, she effectively negates the berserker effects of the Hazard Trigger which also leads to Sento creating the FullFull RabbitTank Bottle.

• The FullFull RabbitTank Bottle (フルフルラビットタンクボトル, Furu Furu Rabitto Tanku Botoru) is a 2-in-1 Fullbottle device that can switch between the full forms of the Rabbit and Tank Fullbottles, granting Build access to use each of the Fullbottles' full potentials. This Fullbottle also negates the side-effect of the Hazard Trigger. Its main weapon is the Fullbottle Buster (フルボトルバスター, Furubotoru Basutā), which has two modes: Buster Blade and Buster Cannon. By inserting up to four Fullbottles into the side of this weapon's barrel, it can activate several finishing moves: Fullbottle Break (フルボトルブレイク, Furubotoru Bureiku) via one Fullbottle, Just Match Break (ジャストマッチブレイク, Jasuto Matchi Bureiku) via two Fullbottles, Miracle Match Break (ミラクルマッチブレイク, Mirakuru Matchi Bureiku) via three Fullbottles, Ultimate Match Break (アルティメットマッチブレイク, Arutimetto Macchi Bureiku) via four Fullbottles, and FullFull Match Break (フルフルマッチブレイク, Furu Furu Matchi Bureiku) via the FullFull RabbitTank Bottle.
  • RabbitRabbit Form (ラビットラビットフォーム, Rabitto Rabitto Fōmu), also known as the "Crimson Speedy Jumper" (紅のスピーディージャンパー, Kurenai no Supīdī Janpā), is Build's speed form which allows him to utilize the full potential of the Rabbit Fullbottle's powers. His finishing move in this form is the Hazard Finish: RabbitRabbit Finish (ハザードフィニッシュ ラビットラビットフィニッシュ, Hazādo Finisshu Rabitto Rabitto Finisshu).
  • TankTank Form (タンクタンクフォーム, Tanku Tanku Fōmu), also known as the "Blue Warrior of Steel" (鋼鉄のブルーウォーリア, Kōtetsu no Burū Wōria), is Build's strength form which allows him to utilize the full potential of the Tank Fullbottle's powers. His finishing move in this form is the Hazard Finish: TankTank Finish (ハザードフィニッシュ タンクタンクフィニッシュ, Hazādo Finisshu Tanku Tanku Finisshu).
• The Genius (ジーニアス, Jīniasu) Fullbottle is a special Fullbottle created by Takumi from a green Pandora Panel that combines the power of all 60 Fullbottles, enabling Build to access his ultimate form, Genius Form (ジーニアスフォーム, Jīniasu Fōmu), also known as the "Completely Flawless Bottle Guy" (完全無欠のボトルヤロー, Kanzen Muketsu no Botoru Yarō). In this form, Build has the ability to perform Hazard purification and can even go toe-to-toe with Evol Black Hole Form via high speed movement. He is also still able to utilize the Fullbottle Buster in this form. If attached with the Hazard Trigger, Build also gains the ability to negate the Pandora Panel's effects on Lost Fullbottles. After the completion of the Pandora Box, Sento loses this form as the Genius Fullbottle returned to its original form. Build's finishing moves in this from are as follows:
  • Genius Attack (ジーニアスアタック, Jīniasu Attaku): Harnessed through the energy of the 30 organic Fullbottles.
  • Genius Break (ジーニアスブレイク, Jīniasu Bureiku): Harnessed through the energy of the 30 inorganic Fullbottles.
  • Genius Finish (ジーニアスフィニッシュ, Jīniasu Finisshu): Harnessed through the energy of all 60 Fullbottles.
• RabbitDragon Form (ラビットドラゴンフォーム, Rabitto Doragon Fōmu) is the special Best Match that Sento developed from Shinobu Katsuragi's samples of Build's Rabbit and Cross-Z's Dragon Fullbottles to create the Gold Rabbit (ゴールドラビット, Gōrudo Rabitto) and Silver Dragon (シルバードラゴン, Shirubā Doragon) Fullbottles by the events of Be the One for the purpose of destroying Evolto. As a Trial Form, this form's finishing move is the Vortex Attack but it has a late Best Match announcement on the Build Driver due to Sento's own resolve.
  • Cross-ZBuild Form (クローズビルドフォーム, Kurōzu Birudo Fōmu) is an enhanced form of Build's RabbitDragon Form that appears in Be The One, using the Cross-ZBuild Can (クローズビルド缶, Kurōzu Birudo Kan) that Vernage created by temporary fusing the Genius Bottle with the Gold Rabbit and Silver Dragon Fullbottles. Sento assumes the form while absorbing Ryūga during their fight against Kamen Rider Blood. After the three tribesmen's defeat, the Cross-ZBuild Can separated back into three components. His finishing move is the Love and Peace Finish (ラブ&ピースフィニッシュ, Robu Ando Pīsu Finisshu).

These forms only appears in other media:

• KumaTelevi Form (クマテレビフォーム, Kuma Terebi Fōmu), also known as the "Honey High Vision" (はちみつハイビジョン, Hachimitsu Hai Bijon), is a Best Match that is accessed via the Kuma (クマ, Bear) and Televi (テレビ, Terebi, Television) Fullbottles. In this form, Build is armed with a giant claw that allows him to generate honey, and gains assistance in the form of an artificial intelligence Televi-san (てれびさん, Terebi-san). This Best Match is currently exclusive to Kamen Rider Build: Birth! KumaTelevi!! Vs. Kamen Rider Grease.
• SameBike Form (サメバイクフォーム, Same Baiku Fōmu), also known as the "Solo-Running Hunter" (独走ハンター, Dokusō Hantā), is a Best Match that is accessed via the Same (サメ, Shark) and Bike (バイク, Baiku) Fullbottles. This form provides Build with echolocation and summoning energy constructs of Machine Builder. This Best Match is exclusive to Kamen Rider Build: Raising the Hazard Level With 7 Best Matches. In the series proper, Utsumi was revealed to sabotage the Kaiser Systems from the very start and programmed SameBike Fullbottles as its counteract, having used it to destroy Evolto's replica of Hell Bros.
• BeetleCamera Form (ビートルカメラフォーム, Bītoru Kamera Fōmu), also known as the "Scoop King of the Forest" (密林のスクープキング, Mitsurin no Sukūpu Kingu), is a Best Match that is accessed via the Kabutomushi (カブトムシ, Rhinoceros beetle) and Camera (カメラ, Kamera) Fullbottles. This Best Match is exclusive to the Ganbarizing video game.
• DogMic Form (ドッグマイクフォーム, Doggu Maiku Fōmu), also known as the "Big Sound of Healing" (癒しの大爆音, Iyashi no Daibakuon), is a Best Match that is accessed via the Dog (ドッグ, Doggu) and Mic (マイク, Maiku) Fullbottles. This Best Match is exclusive to the Ganbarizing video game.
• MerryChristmas Form (メリークリスマスフォーム, Merī Kurisumasu Fōmu), also known as the "Holy Emissary" (聖なる使者, Seinaru Shisha), is a Best Match that is accessed via the Santa Claus (サンタクロース, Santa Kurōsu) and Cake (ケーキ, Kēki) Fullbottles. This Best Match is exclusive to the Ganbarizing video game.
• UniRaser Form (ユニレイサーフォーム, Yuni Reisā Fōmu), also known as the "One-Horned Erasure" (一角消去, Ikkaku Shōkyo), is a Best Match that is accessed via the Unicorn (ユニコーン, Yunikōn) and Keshigomu (消しゴム, Keshigomu, Eraser) Fullbottles. This Best Match is exclusive to the Ganbarizing video game.
• ShikaMid Form (シカミッドフォーム, Shika Middo Fōmu), also known as the "Royal Family Guardian" (王家の守り神, Ōke no Mamorigami), is a Best Match that is accessed via the Shika (シカ, Deer) and Pyramid (ピラミッド, Piramiddo) Fullbottles. This Best Match is exclusive to the Ganbarizing video game.
• PenguinSkater Form (ペンギンスケーターフォーム, Pengin Sukētā Fōmu), also known as the "Ice Sliding Peformer" (氷のスベり芸, Kōri no Suberi-gei), is a Best Match that is accessed via the Penguin (ペンギン, Pengin) and Sukebo (スケボー, Sukebō, Skateboard) Fullbottles. This Best Match is exclusive to the Ganbarizing video game.
• MagGhost Form (マグゴーストフォーム, Magu Gōsuto Fōmu), also known as the "Wandering Attraction" (彷徨える超引力, Samayoeru Chōinryoku), is a Best Match that is accessed via the Obake (おばけ, Ghost) and Magnet (マグネット, Magunetto) Fullbottles. This Best Match is exclusive to the Ganbarizing video game.
• Legend Rider Best Match Forms: Much like Kamen Rider Decade before him, Build can shape-shift into the primary forms of any of the previous lead Kamen Riders via Best Match function between two corresponding Fullbottles based the previous lead Riders' motifs. In the Kamen Rider Battle: Ganbarizing video game, if Build uses different Legend Rider Fullbottles for Trial Forms, Build will not shape-shift into the previous lead Kamen Riders. Most Legend Rider-themed Fullbottles have a compatible Best Match with one of Build's regular Fullbottles.
  • Ex-Aid Form (エグゼイドフォーム, Eguzeido Fōmu): By using the Doctor (ドクター, Dokutā) and Game (ゲーム, Gēmu) Fullbottles, Build shapeshifts into Kamen Rider Ex-Aid Action Gamer Level 2 where he is armed with the Gashacon Breaker. When purified, the Ex-Aid (エグゼイド, Eguzeido) Fullbottle split into the two Fullbottles. This Best Match is exclusive to Kamen Rider Heisei Generations Final: Build & Ex-Aid with Legend Rider.
  • Ghost Form (ゴーストフォーム, Gōsuto Fōmu): By using the Obake and Parka (パーカー, Pākā) Fullbottles, Build shapeshifts into Kamen Rider Ghost Ore Damashii where he is armed with the Gan Gun Saber. This Best Match is exclusive to the Ganbarizing video game.
  • Gaim Form (鎧武フォーム, Gaimu Fōmu): By using the Orange (オレンジ, Orenji) and Lock Fullbottles, Build shapeshifts into Kamen Rider Gaim Orange Arms where he is armed with both the Daidamaru and the Musou Saber. This Best Match is exclusive to the Ganbarizing video game.
  • Wizard Form (ウィザードフォーム, Wizādo Fōmu): By using the Mahoutsukai (魔法使い, Mahōtsukai, Magician) and Diamond Fullbottles, Build shapeshifts into Kamen Rider Wizard Flame Style where he is armed with the Wizarswordgun. This Best Match is exclusive to the Ganbarizing video game.
  • Fourze Form (フォーゼフォーム, Fōze Fōmu): By using the Yujou (友情, Yūjō, Friendship) and Rocket Fullbottles, Build shapeshifts into Kamen Rider Fourze Base States where he gains the ability to manifest an Astroswitch's Fourze Module onto his limbs. This Best Match is exclusive to the Ganbarizing video game.
  • OOO Form (オーズフォーム, Ōzu Fōmu): By using the Taka and Medal (メダル, Medaru) Fullbottles, Build shapeshifts into Kamen Rider OOO Tatoba Combo where he is armed with both the Medajalibur and the Medagabryu. This Best Match is exclusive to the Ganbarizing video game.
  • Double Form (Wフォーム, Daburu Fōmu): By using the Tantei (探偵, Detective) and USB Memory (USBメモリ, Yū Esu Bī Memori) Fullbottles, Build shapeshifts into Kamen Rider Double CycloneJoker. This Best Match is exclusive to the Ganbarizing video game.
  • Decade Form (ディケイドフォーム, Dikeido Fōmu): By using the Card (カード, Kādo) and Camera Fullbottles, Build shapeshifts into Kamen Rider Decade where he is armed with the Ride Booker. This Best Match is exclusive to the Ganbarizing video game.
  • Den-O Form (電王フォーム, Den'ō Fōmu): By using the Momotaros (モモタロス, Momotarosu) and Densya Fullbottles, Build shapeshifts into Kamen Rider Den-O Sword Form where he is armed with the DenGasher. This Best Match is exclusive to the Ganbarizing video game.

Sento Kiryū is portrayed by Atsuhiro Inukai (犬飼 貴丈, Inukai Atsuhiro), who also portrays Tarō Satō.

Ryūga Banjō

Ryūga Banjō (万丈 龍我, Banjō Ryūga) is a 23-year old ex-fighter who was born in Yokohama. Prior to his birth, a portion of Evolto's essence, which had come to Earth via a Martian probe, fused with the unborn Ryūga in a failed attempt to possess his mother Yuri Banjō (万丈 優里, Banjō Yuri), who was a security guard for the probe exhibit. As a result, Ryūga was born after only two months of gestation, and spent much of his childhood being tested by Namba Industries. Ryūga lost his parents in an accident at the age of 13, and he blames the resulting drama for his lack of memories of them. He eventually became a professional fighter until getting a lifetime ban for throwing a match. He was supposed to work with the former Touto Institute researcher and founder of Faust, Takumi Katsuragi. Takumi learned of Ryūga's nature while quitting Faust, hiring Ryūga under false pretenses as he knew Evolto intended to transfer himself from Sōichi Isurugi into Ryūga, so he intended to kill them both. But Takumi's plan backfires, with Evolto having Ryūga arrested for Takumi's apparent death with a 10-year jail sentence. While in prison, Ryūga was kidnapped by Faust's agent Nabeshima to be used for experimentation. Due to his half-alien physiology, he managed to escape with his humanity intact. After escaping, he is found by Sento who takes him under his protection in the hopes of getting clues to his past. Shortly after, Ryūga is forced to watch his girlfriend Kasumi Ogura be turned into a Smash, eventually dying due to her low Hazard Level. Sento gave him the Dragon Fullbottle containing her Smash essence as a keepsake, and later a small robotic dragon-like companion to assist Ryūga known as the Cross-Z Dragon (クローズドラゴン, Kurōzu Doragon).

Sento eventually gave Ryūga a copy of the Build Driver, after which he adopted the mantle of Kamen Rider Cross-Z (仮面ライダークローズ, Kamen Raidā Kurōzu). As time passed on, Ryūga would gradually receive upgrades but instead of simple form changes, his were evolutions of Cross-Z. Ryūga later learns of his true origins from Vernage while having been manipulated by Evolto's machinations to strengthen his alien genes as part of the entity's plan to possess him.

During the events of the film Be the One, manipulated by Kengo Inō to attack Sento, Ryūga played a role in Sento's ability to assume Build's Cross-Z Build Form when the Kamen Rider absorbed him so they can defeat Kamen Rider Blood together.

In the final clash against Evolto, Ryūga sacrifices himself to restrain a weakened Evolto as they are sucked into a wormhole created by the complete Pandora Box, with Evolto absorbing him in a final attempt to survive before Sento frees Ryūga as the alien is permanently destroyed. Due to Sento's actions, the Pandora Box transports Ryūga into the "Prime" Kamen Rider world after it absorbed his reality and was found by Sento after running into the prime universe's Ryūga, who is still an active sports fighter and in a relationship with his reality's Kasumi. Ryūga then joins Sento in making a new life for themselves in this new reality.

Thanks to Ryūga's alien origins and the experiments done on him by Faust, he has extraordinary abilities such as increased strength, being able to raise his Hazard Level faster than usual and manipulating the Pandora Box. Once reaching Hazard Level 7, Ryūga transformed the Dragon Fullbottle into the Silver Dragon Fullbottle. Although a strong fighter, Ryūga is easily provoked and not too bright. However, he was kind-hearted and generally puts others before himself. During Evolto's awakening of Phase 4, Cross-Z suffers from uncontrollable rage of his past life as Evolto, which also granted him the power of manipulating black holes at a smaller rate before they were ultimately neutralized when Vernage's essence was transferred into him during Misora's rescue.

• The original Kamen Rider Cross-Z is transformed by inserting the Dragon Fullbottle into Cross-Z Dragon and in turn inserted into the Build Driver. Aside from gaining symmetrical Halfbodies, Cross-Z obtains Drago Live Razor (ドラゴライブレイザー, Dorago Raibu Reizā) torso armor that allows him to channel Cross-Z Dragon Blaze (クローズドラゴン・ブレイズ, Kurōzu Doragon Bureizu) energy flames as attacks and empowering his finishing move, Dragonic Finish (ドラゴニックフィニッシュ, Doragonikku Finisshu). Unlike Build, Cross-Z can utilize the Dragon Fullbottle's powers due to the Cross-Z Dragon negating its side effects. His main weapon is the sword-like Beat Closer (ビートクローザー, Bīto Kurōzā), which allows him to initiate one of three special attacks: Smash Hit (スマッシュヒット, Sumasshu Hitto), Million Hit (ミリオンヒット, Mirion Hitto), or Mega Hit (メガヒット, Mega Hitto). Like the Drill Crusher, the Beat Closer can also hold a Fullbottle for Cross-Z to perform one of three Special Tune (スペシャルチューン, Supesharu Chūn) finishing moves: Smash Slash (スマッシュスラッシュ, Sumasshu Surasshu), Million Slash (ミリオンスラッシュ, Mirion Surasshu), or Mega Slash (メガスラッシュ, Mega Surasshu). Said weapon is usually empowered by his Lock Fullbottle.
• Kamen Rider Cross-Z Charge (仮面ライダークローズチャージ, Kamen Raidā Kurōzu Chāji): A silver-colored upgrade that was accessed by the finalized Sclash Driver (スクラッシュドライバー, Sukurasshu Doraibā) and a Dragon Sclashjelly (スクラッシュゼリー, Sukurasshu Zerī). Sento was meant to use it at the height of Hokuto's invasion on Touto but was forced to relinquish it to Ryūga for his higher Hazard Level. His finishing move is the Scrap Break (スクラップブレイク, Sukurappu Bureiku). Cross-Z Charge's main weapon is the Twin Breaker (ツインブレイカー, Tsuin Bureikā), which has a laser gun-like Beam Mode and a jackhammer-like Attack Mode. Unlike the Drill Crusher and Beat Closer, the Twin Breaker can hold up to two Fullbottles and Sclashjellies, as well as either the RabbitTank Sparkling or the Cross-Z Dragon, for Cross-Z Charge to perform its finishing move. Inserting an organic Fullbottle into the Sclash Driver allows Cross-Z Charge to initiate the Charge Crash (チャージクラッシュ, Chāji Kurasshu), having once utilized the Taka Fullbottle for flight purposes. However, usage of the Sclash Driver exposes Ryūga to unfiltered Nebula Gas which causes him to become aggressive until his determination and guilt over causing Sento to use the Hazard Trigger finally gives him the strength to overcome the effects. This form was lost when Ryūga shielded Vernage at the cost of Dragon Sclashjelly. Although another Dragon Sclashjelly was created, it was given to Grease as Cross-Z favors his later upgrades instead.
• Kamen Rider Cross-Z Magma (仮面ライダークローズマグマ, Kamen Raidā Kurōzu Maguma): Also known as the "Extreme Heat Muscle" (極熱筋肉, Gokunetsu Kinniku), it is Cross-Z's super form, accessed by inserting the Cross-Z Magma Knuckle (クローズマグマナックル, Kurōzu Maguma Nakkuru) loaded with the Dragon Magma (ドラゴンマグマ, Doragon Maguma) Fullbottle into the Build Driver. Although its purpose as an upgraded form was envisioned, further developments were put on hold as the three Riders tried to storm the Pandora Tower until Ryūga's own resolve completed the Dragon Magma Fullbottle as the final component. By himself, Cross-Z Magma can channel Variable Magma (ヴァリアブルマグマ, Variaburu Maguma) as empowerment for attacks, creating snake dragon constructs and manifesting a pair of wings for flight. His finishing move in this form is the Volcanic Finish (ボルケニックフィニッシュ, Borukenikku Finisshu). With the Cross-Z Magma Knuckle as a handheld weapon, he can perform the Volcanic Knuckle (ボルケニックナックル, Borukenikku Nakkuru) by channeling the power of any Fullbottles it utilized. Before relinquishing it to Grease, Cross-Z Magma was briefly in possession of the incomplete Blizzard Knuckle (ブリザードナックル, Burizādo Nakkuru), having given a hand in its creation. With the Silver Dragon Fullbottle, he can perform Glacial Knuckle (グレイシャルナックル, Gureisharu Nakkuru) and weakening Evolto's DNA. In the final battle on Pandora Tower, Build lent Cross-Z Magma the Hazard Trigger, which allows him to fight on par with Evol Black Hole Form before the latter's transition into his monster form.
• Kamen Rider Great Cross-Z (仮面ライダーグレートクローズ, Kamen Raidā Gurēto Kurōzu): An upgraded variant of the original Cross-Z, accessed by inserting the Great Cross-Z Dragon (グレートクローズドラゴン, Gurēto Kurōzu Doragon) loaded with the Great Dragon (グレートドラゴン, Gurēto Doragon) Evol-Bottle into the Build Driver. Having lost Evolto's genes on his body after his liberation from possession, Ryūga regains it by stealing the Dragon Evol-Bottle as it upgraded into its current form. His finishing move in this form is the Great Dragonic Finish (グレートドラゴニックフィニッシュ, Gurēto Doragonikku Finisshu).
• Kamen Rider Cross-Z Evol (仮面ライダークローズエボル, Kamen Raidā Kurōzu Eboru): Also known as the "The Invincible Galaxy Muscle Guy" (銀河無敵の筋肉野郎, Ginga Muteki no Kinniku Yarō), is Cross-Z's final form accessed by using the Muscle Galaxy Fullbottle in the Build Driver. It combines the power of Cross-Z and Evol, invoking Evol's Black Hole Form. It's finshing moves includes:Muscle Finish (マッスルフィニッシュ, Massuru Finisshu), Galaxy Finish (ギャラクシーフィニッシュ, Gyarakushī Finisshu), Muscle Galaxy Finish (マッスルギャラクシーフィニッシュ, Massuru Gyarakushī Finisshu). This form is exclusive to Kamen Rider Build NEW WORLD: Kamen Rider Cross-Z.

Ryūga Banjō is portrayed by Eiji Akaso (赤楚 衛二, Akaso Eiji).

Misora Isurugi

Misora Isurugi (石動 美空, Isurugi Misora) is a 19-year-old girl and Sōichi's daughter who works as Sento's assistant, gaining a supernatural power after being rendered comatose for seven years from being exposed to the Pandora Box sometime after the Skywall Disaster. She would be revealed to have played a role in Project Build, as Evolto used Sōichi's memories of her drawings of organic and inorganic-based objects to influence Shinobu in developing the Best Match aspect of the technology. She was kidnapped by Faust to use in their traumatic experimentation until Sōichi managed to rescue her a year ago. Fearing that Faust is still trailing her, she remained in Nascita while using her online idol identity Mii-tan (みーたん, Mītan) to gather Smash intel and occasionally money from her fanbase. But Misora was unaware that her father is actually a high-ranking Faust agent who used her, Sento and Ryūga as their tools to create a Kamen Rider army within Touto. Though Sento, Ryūga and Sawa decide to spare Misora from knowing her father's activities in Faust upon learning he is Blood Stalk, she is hinted to have learned this revelation as well while being driven to despair. She later uses her powers to cure Taizan Himuro of Sōichi's poison so he can resume his duties as Touto's prime minister and soon discovers that her father is actually being possessed by Evolto, the true villain committing the crimes using her father as a vessel.

Due to being exposed to the Pandora Box, wearing a bracelet that originated from Mars, Misora possesses the ability to purify and enhance Nebula Gas which made her a target for Faust in the first place. Initially, the usage of the ability exhausts her to the point of a week-long sleep before Sento developed a machine that would reduce her burden. Misora later awakens her full potential when nearly killed by a berserk Build Hazard Form, allowing her to purify the higher Nebula Gas concentrations like those from the Hazard Trigger itself. Sento would use her power to create the FullFull RabbitTank Bottle and Fullbottle Buster to negate the Hazard Trigger's side-effects. During Seito's invasion, the bracelet is revealed to house the spirit of the Martian Vernage who is revealed to be the source of Misora's power. Misora was later kidnapped by Evolto and turned into the CD Lost Smash (CDロストスマッシュ, Shī Dī Rosuto Sumasshu) that can throw Glare Slicer (グレアスライサー, Gurea Suraisā) discs, Sento managing to restore Misora by extracting Vernage to render the girl completely human and transferring the alien into Ryūga.

After Sento merged his world with that of the "Prime" Kamen Rider universe in the aftermath of Evolto's defeat, an alternate Misora is shown to be a waitress at her father's café.

Misora Isurugi is portrayed by Kaho Takada (高田 夏帆, Takada Kaho). As a child, Misora is portrayed by Noel Moriyama (森山 のえる, Moriyama Noeru).

Sawa Takigawa

Sawa Takigawa (滝川 紗羽, Takigawa Sawa) is a 27-year-old freelance journalist dedicated to learning about Build and the Smash since being saved by the former after he saved her from the Needle Smash, later learning of the Kamen Rider's true identity as Sento and providing him with assistance. While later revealed to be a spy for Namba, Sawa is actually using her position to covertly learn the truth behind the cover-up of an industrial accident at Namba Heavy Industries that killed her father and ten others. When Misora exposed her cover, Sawa is punished by being turned into the octopus-themed Stretch Smash (ストレッチスマッシュ, Sutoretchi Sumasshu) before she is defeated by Ryūga with Sento extracting the Nebula Gas from her system. After that, she decides to atone for her actions and join forces with Sento's group to fight against Namba and Faust. During the time she spent with them, Sawa becomes protective of Misora, especially after learning of the younger woman's past.

Sawa is later revealed to be a Namba Child agent, the story about her father being a fabrication. She was supposed to let herself be disposed of under Namba's instructions after failing her mission but the familial bonds she made with Sento and the others gave her a reason to live and influenced her decision to completely cut ties with Namba. Sawa accomplishes this by aiding Sento in the ploy to trick Namba by giving him a fragment of Sento's research on the FullFull RabbitTank Bottle while Kazumi rescues the Nabeshima family whom Namba was held hostage as leverage against her, finally freeing herself from Namba's control. She later helps take care of Sōichi, who had entered a coma after Evolto releases him from his control.

After Sento merged his world with that of the "Prime" Kamen Rider universe, an alternate Sawa is shown to also be working as a journalist. She nervously passed a business card to this new world's version of Gentoku for an interview, with the latter agreeing to it along with a dinner date which she accepted, in complete contrast to their counterparts' first encounter at the start of the series.

Sawa Takigawa is portrayed by Yukari Taki (滝 裕可里, Taki Yukari).

Sōichi Isurugi

Sōichi Isurugi (石動 惣一, Isurugi Sōichi) is the rather enigmatic 48-year-old owner of nascita and Misora's father who is actually Faust's high-ranking member Blood Stalk (ブラッドスターク, Buraddo Sutāku). He is a kind-hearted man and a good friend to Takumi's father Shinobu Katsuragi. Ten years prior to the series, he was the astronaut who discovered the abandoned Evol Driver, and eventually the Pandora Box on Mars, resulting in his possession by the evil entity Evolto who subjugated his mind while using the man's body to commit numerous atrocities from causing the Skywall Disaster by coming in contact with the Pandora Box to frame Shinobu, manipulating Takumi's current identity Sento and Sōichi's daughter Misora for his own ends. But Sōichi's personality resurfaces on occasion, having briefly surfaced in an attempt to fight Evolto before being suppressed. Sōichi was later tricked by Evolto into thinking that the alien would leave his body upon retrieving the Evol Driver, ending up in a coma and taken under Sawa's care while Evolto possesses Ryūga and Sento consecutively to get what he needed from them before creating his own body in Sōichi's image for his end game. After Sento merged his world with that of the "Prime" Kamen Rider universe, an alternate Sōichi is shown as an actual café-owner running nascita who mistakes Sento for Tarō Satō.

Due to being possessed by Evolto, Sōichi gains several inhuman abilities. He can transmute matter, as shown when he transformed his tablet computer into pieces of paper. He can also mold a person's face into that of another person while also manipulating their memories, he is also able to return his original face to a person once he changes it. He is also shown to be capable of quickly leaping into the air to escape.

With Evolto possessing him, Sōichi uses the Cobra (コブラ, Kobura) Fullbottle to transform into Blood Stalk. As Blood Stalk, he is a skilled fighter who can poison his opponents by stabbing them with an appendage, as well as hacking Touto's Guardians with a simple flick. Through his animal motif, he can summon a projection of a large cobra for various applications. With the Devil Steam, he is able to either release Nebula Gas to change regular people into Smash via the Steam Blade or inject a Smash with a Nebula Gas-filled bullet to enlarge them into giants via the Steam Rifle. Via Rocket Fullbottle, Stalk can launch guided energy missiles.

Sōichi Isurugi is portrayed by Yasuyuki Maekawa (前川 泰之, Maekawa Yasuyuki).

Kazumi Sawatari

Kazumi Sawatari (猿渡 一海, Sawatari Kazumi) is a 29-year-old soldier from Hokuto and the current owner of his farm. In hopes of obtaining more financial support, Kazumi willingly signed for Hokuto's military and underwent Faust's human experimentation. Lying about suffering memory loss, Kazumi's continued use of the Sclash Driver turned him into a bloodthirsty fighter, though he was able to keep his bloodlust under control. However, he despises cruelty and is above harming civilians, as he saw himself as nothing more than a soldier going to war and threatened his own Prime Minister for ordering Hokuto's troops to target innocent people during their invasion of Touto. He also cares for his co-workers' welfare and was visibly upset when the Hokuto Three Crows underwent additional Nebula Gas infusion, knowing that their next defeat will guarantee their deaths. He is also a fan of Misora, having watched her performances alongside his co-workers in the past.

Having first infiltrated Touto during the events of Heisei Generations Final to reclaim Build's Phoenix and Robot Fullbottles for Hokuto, Kazumi is deployed to lead the Hokuto army to invade Touto. The conflict eventually ends in a decisive battle with Grease defeated by Build HawkGatling Hazard and Cross-Z Charge saving Grease from being killed at the last second when Sento goes berserk thanks to the Hazard Trigger. During Seito's attack on his country and Touto, he join forces with the crews of nascita in hopes of reclaiming Hokuto. As the series passed, he slowly moving on with the deaths of Three Crows while making peace with two of their killers, Sento and Gentoku, though he takes a longer time to do so with Gentoku as the latter had killed Akaba by his own choice while Sento killing of Aoba was the result of the Hazard Trigger inducing him into a berserk rage. In hopes of catching up with Build and Cross-Z's rise of strength, Kazumi and Gentoku allowed themselves to be kidnapped and forcefully raising their Hazard Levels while putting their lives at risk.

After Evolto reveals his true plans, Kazumi fought alongside the Touto Riders in order to put an end to the genocidal alien. During that time, Sento had created a copy of Cross-Z's Magma Knuckle called the Blizzard Knuckle for Grease as a power-up, but made it incompatible with Schlash Driver as Kazumi's heightened Hazard Level being subjected to multiple infusions of Nebula Gas would make its use fatal. But when facing powerful replicas of the Three Crows which Evolto created as his enforcers, Kazumi reveals that he had taken Shinobu's Build Driver and uses the Blizzard Knuckle to transform into Kamen Rider Grease Blizzard, knowing full well that he was going to die, to destroy the copies before succumbing to his transformation's side effect as he dissipates in Misora's arms.

After Sento merged his world with that of the "Prime" Kamen Rider universe in the aftermath of Evolto's defeat, an alternate Kazumi and the Hokuto Three Crows are shown paying a visit to nascita where the Crows try to set him up with Misora who in this new world is a waitress. Kazumi, however, falls in love with Misora and faints from excitement after seeing her for the first time, causing the Crows to carry him out.

By himself, the injection of Nebula Gas allows Kazumi to utilize a Fullbottle's power on a smaller rate, which was enough to incinerate a Hazard Smash. His alter-ego, Kamen Rider Grease (仮面ライダーグリス, Kamen Raidā Gurisu), was created based on the statistic of Robot Fullbottle.

• The original Kamen Rider Grease is transformed through the use of the Sclash Driver and Robot Sclashjelly, with his finishing move being the Scrap Finish (スクラップックフィニッシュ, Sukurappu Finisshu). His main weapon is the Twin Breaker, which allows him to channel the power of either two Fullbottles or one mixed with his Robot Sclashjelly. By inserting an inorganic Fullbottle into the Sclash Driver, Grease can perform the Discharge Crash (ディスチャージクラッシュ, Disuchāji Kurasshu), manifesting Variable Jelly (ヴァリアブルゼリー, Variaburu Zerī) per various attacks or means of transportation. Before receiving his own upgraded form, Grease was provided another Dragon Sclashjelly, allowing him to utilize another copy of the Twin Breaker and therefore saving his life from disappearing as a result of his heightened Hazard Level.
• Kamen Rider Grease Blizzard (仮面ライダーグリスブリザード, Kamen Raidā Gurisu Burizādo): Also known as the "Frozen Soul Fire" (激凍心火, Gekitō Shinka), it is accessed by inserting the Grease Blizzard Knuckle (グリスブリザードナックル, Gurisu Burizādo Nakkuru) loaded with the North Blizzard (ノースブリザード, Nōsu Burizādo) Fullbottle into the Build Driver that originally belonged to Shinobu. In this form, Grease Blizzard is armed with the GBZ Demolition One (GBZデモリションワン, Jī Bī Zetto Demorishon Wan) on his left arm and can generate Variable Ice (ヴァリアブルアイス, Variaburu Aisu) frozen liquid to empower his attacks. The GBZ Demolition One allows him to initiate the Glacial Break (グレイシャルブレイク, Gureisharu Bureiku), whereas his true finishing move is the Glacial Finish (グレイシャルフィニッシュ, Gureisharu Finisshu). The Grease Blizzard Knuckle was created by Sento as a counteract for Evolto, based on sample of his genes via Ryūga. Initially wielded by Cross-Z Magma, Kazumi was given the weapon alongside the North Blizzard Fullbottle created by his and the Hokuto Three Crows' feedback data. Against Sento's warning that it would kill him, Grease used this form as a last resort tactic and died as a result.

Kazumi Sawatari is portrayed by Kouhei Takeda (武田 航平, Takeda Kōhei). The numbers on his character's dog tags are a play on the name of a character he previously portrayed in Kamen Rider Kiva, Otoya Kurenai.

Hokuto Three Crows

The Hokuto Three Crows (北都三羽ガラス, Hokuto Sanba Garasu) are a group of Hokuto soldiers who were originally workers of Kazumi Sawatari's farm and enlisted into Hokuto's military to repay their former employer's debt for financially supporting their families. Using Shinobu Katsuragi's Lost Bottles, each are able to transform into enhanced form of the Smash known as Hard Smash (ハードスマッシュ, Hādo Sumasshu) and later the stronger Hazard Smash (ハザードスマッシュ, Hazādo Sumasshu), which gave increased strength but killed the user if they are knocked out of a transformation. Following their deaths, Grease kept their Bottles as memorabilia and had once combined their energies to perform a stronger attack. Evolto later creates corrupted copies of them to serve as his enforcers, but they were destroyed by Kamen Rider Grease at the cost of his own life.

Gentoku Himuro

Gentoku Himuro (氷室 幻徳, Himuro Gentoku) is the 35-year-old special advisor to his father, Prime Minister Taizan Himuro, and head of the Touto Institute. Initially a kind, friendly and rather laid-back eccentric man with an odd fashion sense, the radiation of Nebula Gas from Skywall Disaster transformed him into a sadist and paranoid power-hungry maniac, whose concern towards Touto's safety forced him to perform various questionable acts after deeming his father's pacifism a liability. In the early days of founding Faust, Gentoku orchestrated Takumi's expulsion from Touto Institute as a way of covering the Devil Scientist's trails into joining him while unknowingly being manipulated by Sōichi Isurugi (and by extension, Evolto and Namba himself). After taking his late friend's position as the Advisor of Prime Minister, Gentoku took the mantle of Night Rogue and declared his leadership to Faust members.

When Takumi had his identity changed into Sento and Ryūga escaping Faust's capture, Gentoku took advantage of this situation to gather more Fullbottles, perfecting most of Takumi's Rider Systems and reclaiming the Pandora Box after Stalk overthrows him. In exchange of having his identity exposed, Gentoku was elevated into the rank of Prime Minister after Stalk incapacitated his father and forced the two Kamen Riders to be inducted into Touto's military. After sending Cross-Z Charge in leading an invasion against a defenseless Hokuto exposed, he was dismissed by a recovered Taizan and sentenced to exile. This forced him to seek refuge in Namba Heavy Industries and sold his pride by serving Seito's military as Kamen Rider Rogue. The experiment Gentoku received to raise his Hazard Level rendered him a near-emotionless nihilist with a restraining chip to ensure total obedience, while at the same time reversing the negative effects from the radiation of Skywall Disaster. Although working under Namba's servitude, Gentoku exploited multiple openings to assist the Riders in various ways without blowing his cover. During an operation to rescue Taizan, Sento deactivated the restraining chip, allowing Gentoku to return but this came at the cost of Evolto regaining his power as Kamen Rider Evol. After Taizan sacrifices himself to save his life, Gentoku, encouraged by his father's last words, finally begins to seek redemption by allying himself with the other Riders against Evolto and Namba. As the series progressed, the redeemed Gentoku begins to take responsibility and atone his past actions, eventually coming to terms with Sento and Kazumi while reverting to his true personality.

Since the early days of Faust, Gentoku's Hazard Level 3 provides him with the access to transform with the Transteam System. Since the Transteam System was meant as a training dummy to Rider System, his Hazard Level remains uncapped until the experimentation he received from Namba Heavy Industries raised it to Level 4, allowing him to use the Sclash Driver. In hopes of catching up with the growth of Build and Cross-Z, both Kazumi and Gentoku allowed themselves to be captured and heavily dosed with the Nebula Gas to raise their Hazard Levels, which comes with the risk of putting their lives in jeopardy should they be defeated in battle. As the battle against Evolto reaches the climax, Gentoku is distraught when Utsumi sacrifices himself to protect him and Sawa, and then learning that Kazumi had fallen in battle. He ultimately dies protecting everyone else during a clash with Evolto, successfully landing a critical blow on the evil alien. As he dissipates, Gentoku's last thoughts were that of his father, and the shadow he cast changed to that of his Kamen Rider form, suggesting his full redemption.

After Sento merged his world with that of the "Prime" Kamen Rider universe, an alternate Gentoku is shown working with his father as his personal aide, and displays a shy but polite attitude towards his world's version of Sawa as he agreed to do an interview with her over a dinner date, which contrasts their counterparts' first encounter in the other reality where he made aggressive advances towards her.

• Night Rogue (ナイトローグ, Naito Rōgu): Gentoku's first transformation as the leader of Faust, accessed through the use of the Transteam Gun loaded with the Lost Bottle counterpart of the Bat Fullbottle. Aside from being a skilled combatant, he can manipulate steams from his body for quick travel and summoning electrical energy to create an energy punch. Through his animal motif, he is capable of clinging to ceilings and summon a pair of bat wings from his back, allowing him to swoop about at high speeds while performing powerful dive-bomb attacks. These items were relinquished to Utsumi once Gentoku became Kamen Rider Rogue.
• Kamen Rider Rogue (仮面ライダーローグ, Kamen Raidā Rōgu): Gentoku's recent alter-ego, accessed through the use of the Sclash Driver in conjunction with the Crocodile Crack (クロコダイルクラック, Kurokodairu Kurakku) Fullbottle. Having strength that rivals even Build's Hazard forms, he is armed with the Nebula Steam Gun. Using the Sclash Driver, Rogue can perform the Crack Up Finish (クラックアップフィニッシュ, Kurakku Appu Finisshu) finishing move. Using the Nebula Steam Gun, he can perform two finishing moves; the Funky Break (ファンキーブレイク, Fankī Bureiku) in its Gun Mode or the Funky Shot (ファンキーショット, Fankī Shotto) in its Rifle Mode. As with the general function of both Sclash Drivers and Nebula Steam Gun, Gentoku can utilize the power of a single Fullbottle and auxiliary attacks.
• Kamen Rider Prime Rogue (仮面ライダーロープライムローグ, Kamen Raidā Puraimu Rōgu): An upgraded form of Kamen Rider Rogue, accessed by using the Prime Rogue Fullbottle in the Build Driver. This form is exclusive to Kamen Rider Prime Rogue.

Gentoku Himuro is portrayed by Kensei Mikami (水上 剣星, Mikami Kensei).

Faust agents

Guardians

The Guardians (ガーディアン, Gādian) are enforcement androids mass-produced by Namba Industries as peacekeepers of each country. At first, only Touto is seemingly able to build Guardians, until the revelation that Namba has been supporting the other two governments as well. They also act as sleeper agents of Faust and their true programming can be activated by Blood Stalk.

They are armed with the Safeguard Rifles (セーフガードライフル, Sēfugādo Raifuru) and ride motorcycles called Capital Roaders (キャピタルローダー, Kyapitaru Rōdā). A large number of them can combine together to form a single gigantic robot equipped with multiple guns. Under Faust's servitude, the removal of safety panels allows the reprogrammed Guardians to act as suicide bombers if needed.

Jūzaburō Namba

Jūzaburō Namba (難波 重三郎, Nanba Jūzaburō) is the corrupt and war-mongering chairman of Namba Heavy Industries. Initially appearing to be nothing more than a benefactor for Faust, collaborating with the organization and Evolto from Mars solely to acquire the Build system and use it for military applications, he is revealed to be one of the main antagonists of the series, having been manipulating the three government regions as part of his agenda to use the Pandora Box's energy to create weapons surpassing the world's nuclear arsenal. He also brainwashed various children to serve as his personal army of infiltrators within the three governments, including Sawa Takigawa, although she has since cut all ties with him. A power-hungry man with a god-like complex, he is ruthless and would not hesitate to sacrifice anything and anyone to attain his goals. However, he is not completely cruel as he was shown to be exceptionally close to Nariaki Utsumi in flashbacks despite the fact that the Namba Children were supposed to be his indoctrinated soldiers.

After acquiring the Pandora Box while Hokuto and Seito served their purpose, Namba has Evolto murder Seito's prime minister Masakuni Midō to assume his identity. As a result, a new, youthful Namba regains his mobility as his cover as Seito's prime minister in using the country's resources to begin the construction of Pandora Tower while launching an invasion of Touto. His ultimate goal is to use the power of the Pandora Box to reform Japan, and eventually the entire world, under his own rule and in his own image. Unfortunately, even though he knew how dangerous the Pandora Box's powers are and thus won't open it willingly, Namba realized too late that Evolto exploited him for his own agenda. Namba attempts to request aid from the Kamen Riders as they now have a mutual enemy in Evolto, with only Kazumi refusing to aid him due to their history. But after a fully powered Evolto decimates the Washio Brothers and the Touto Kamen Riders, Namba is killed by Evolto while begging for his life.

Although not seen, after Sento merged his world with that of the "Prime" Kamen Rider universe, an alternate Namba owns a metalworking factory known as Namba Machine Workshop (難波機械製作所, Nanba Kikai Seisakusho) instead of a multi-million weapons manufacturer.

Jūzaburō Namba is portrayed by Akira Hamada (浜田 晃, Hamada Akira), while Norimasa Fuke portrays Namba's disguise as Masakuni Midō.

Namba Children

The Namba Children (難波チルドレン, Nanba Chirudoren) are scientists, soldiers and spies who were brainwashed by Jūzaburō Namba to have complete loyalty to him since they were children. They are positioned as sleeper agents in the factions within Touto, Hokuto, and Seito to serve as Namba's eyes and ears while winning the trust of others to acquire whatever Namba needs.

Hard Guardians

The Hard Guardians (ハードガーディアン, Hādo Gādian) are enhanced versions of the Guardians which Namba Heavy Industries mass-produced in the wake of Seito's war declaration towards Touto. By the time Namba Heavy was disbanded, remaining units fell into Evolto's ownership and serve as the front line of Pandora Tower's defense.

The Hard Guardians are equipped with a combat AI unit, right arm-mounted gatling-guns, left-arm-mounted clawed gauntlets, and shoulder-mounted missile pods. Despite its heavy equipment, an improve drive module was placed on each joints to provide enhanced mobility. Depending on the situation, their equipment can be replaced per combat situations and is able to fight on equal terms against Rider Systems users.

Takumi Katsuragi

Takumi Katsuragi (葛城 巧, Katsuragi Takumi) is a researcher of Touto Institute and the past identity of Sento Kiryū, being the first person to transform into Kamen Rider Build. An emotionless and narcissistic scientist who has problems with expressing gratitude, he gains the moniker of "The Devil's Scientist" (悪魔の科学者, Akuma no kagakusha) from his colleagues for his research in Nebula Gas anomalies. Influenced by the suicide of his father, Takumi became a scientist dedicated to betterment of mankind through the Pandora Box. Takumi revived the experiment as Project Build (プロジェクトビルド, Purojekuto Birudo) to honor his father's memory, but was banned for conducting unethical human experimentations by using a mutative by-product of the Skywall known as Nebula Gas (ネビュラガス, Nebyura Gasu) as a means of evolving humanity. In truth, this was a cover-up made by Gentoku to recruit Takumi and his loyal followers into Faust, therefore erasing any unwanted suspicions on the youth.

During this period, Takumi assisted his former Touto colleague Kaisei Mogami in building the Enigma system for inter-dimensional travel to another reality. While testing the performance of Kamen Rider Build in said world, he intervened on the confrontation between humans and Bugster twice. Having accidentally killed Kamen Rider Genm prior, Build went on to extract Ex-Aid's samples into a single Fullbottle before foiling Mogami's intent to cause a convergence between the two realities and stopped him.

Sometime after developing both Rider and Transteam Systems, Takumi developed a change of heart after learning that Faust has been compromised through an Evolto-possessed Sōichi, including Shinobu's past sins while under direction of that evil martian. This eventually led him to halt the development of the Sclash Driver system and store all his research within a flash drive he sent to his mother. On September 9, Takumi made his move to assassinate both Evolto and Ryūga in one swoop but the former outsmarted him with a malfunctioning prototype of Build Driver, knocking him out and killed Tarō Satō before swapping their faces while having Ryūga as the fall guy of the crime scene. The amnesiac Takumi was renamed as Sento and had since manipulated into completing all of the unfinished plans for Rider System.

More than a year later, Takumi regains his memories when Evolto abandoned Sento's body upon regaining his perfect form. Distraught by the twist of events in his absence, he reclaims the mantle of Build but refuses cooperation from any members of nascita due to his acquired distrust, stemming from how Gentoku and Faust misused his researches to start a civil war in Japan. When the Genius Fullbottle refused to cooperate due to Takumi not being an ideal hero, he was visited by Sento's consciousness and began to put his faith on his new alter-ego, allowing the latter to return in real life and accessing Genius Form for the first time. From that point onward, Takumi would serve as a spiritual adviser to Sento despite his sense of pessimism. After Sento restores the world as a new reality in the aftermath of Evolto's defeat, Takumi finally finds peace and congratulated Sento as he disappears forever from Sento's mind. Although his alternate counterpart did not appear on-screen after Sento merged his world with that of the "Prime" Kamen Rider universe, the official site confirmed that Takumi still works as a scientist in the new world.^[1]

As the true creator of Build's Rider System, Takumi shows no problem in using the basic Best Match forms to his need. Because he was absent for more than a year since Sento had developed Build further into its strongest form, Takumi was forced to retool it for his body to keep up with its performance.

Takumi Katsuragi is portrayed by Yukiaki Kiyama (木山 廉彬, Kiyama Yukiaki), whereas his cameo appearances as Build in Kamen Rider Ex-Aid were voiced by Atsuhiro Inukai, Sento's actor.

Shinobu Katsuragi

Shinobu Katsuragi (葛城 忍, Katsuragi Shinobu) is the father of Takumi Katsuragi and a member of the space program that saw Sōichi Isurugi come to contact with the Pandora Box. He and Takumi were shown to be particularly close to each other, as Shinobu was the reason why Takumi became a scientist. But Takumi was unaware of the full story behind his father overseeing Project Evol following the circumstances of Ryūga's birth, conducting illegal research on the infant, despite using ethical means. Later, Shinobu led the conference of the Pandora Box's discovery when Evolto caused the Skywall Incident, ruining Shinobu's reputation as the newly formed nations of Japan used him as a scapegoat. Shinobu faked his suicide soon after, enlisting Reika Kine's aid in smuggling himself out of Touto while his supposed demise spurred Takumi to dedicate himself improving others' lives as a scientist.

In reality, Shinobu had aided Evolto, who possessed Sōichi, for the next ten years by using his Project Evol research in an attempt to repair the Evol Driver before Takumi found and hid it. Shinobu also developed man-made Evol-Bottles called Lost Bottles (ロストボトル, Rosuto Botoru), which allow the user to transform into a Lost Smash with side-effects of heightened aggression and being easy to manipulate. Shinobu eventually resurfaces while Sento and his allies are searching for the Lost Bottles, revealing his alliance with Evolto while alienating Sento by callously guilt-tripping him in order to convince him that they are enemies. This would be revealed to be a farce Shinobu set up as part of his plan to eliminate the alien and his kin, pretending to be Evolto's ally while creating a specialized Best Match combination based on the data from Build's Rabbit and Cross-Z's Dragon Fullbottles. He reveals his intentions to Sento when he thought Evolto had been defeated, but Evolto, who had caught on to his plan, recovers from his initial defeat and fatally wounds him. Shinobu lives long enough to give Sento his data to finalize as Build's Cross-ZBuild Form, apologizing for hurting him while undercover before dissipating from the effects of Evolto's poison.

It can be assumed that an alternate counterpart of him exist in the new world created by Sento merging his world with that of the "Prime" Kamen Rider universe, as the official site confirms the existence of an alternate Takumi

As the founder of Rider System, Shinobu possesses his own copy of the Build Driver and a set of Fullbottles to transform into another Kamen Rider Build. While having access to Build's basic Best Match forms, Shinobu is capable of outmaneuvering even the strongest of his opponents in one-on-one fights and only has difficulty fighting multiple opponents. Apart from that, he can also use another Fullbottle's power without transitioning into another Best Match, such as the use of Phoenix Fullbottle as an escape while still in RabbitTank form.

Shinobu Katsuragi is portrayed by Zyouzi Kokubo (小久保 丈二, Kokubo Jōji).

Taizan Himuro

Taizan Himuro (氷室 泰山, Himuro Taizan) is the father of Gentoku and the Prime Minister of Touto (東都, Tōto). The country's system of governing and political goals are of traditional pacifism, with only enough military strength for self-defense. Despite the rivalry between all three districts, Taizan wishes for Japan to reunite. Due to his poor health at the time of the unveiling of the Pandora Box, Taizan sent his son Gentoku in his behalf. Thanks to this, he was the only Prime Minister who was not affected by its radiation and managed to retain his sanity. During Faust's raid on Touto facility, Taizan ended up having a heart attack, and entrust his son to take care of Touto during his absence. However, unbeknownst to Taizan, his son is secretly one of Faust's high-rank member, Night Rogue. With Gentoku now in charge, Faust had managed to completely compromise the Touto government until Sento and Ryūga finally defeat Night Rogue, exposing his identity to Taizan who then orders his son to be taken into custody while apologizing to the Riders for the trouble Gentoku had caused them. Unfortunately, Sōichi later poisoned Taizan causing him to fall unconscious which once again gives Gentoku emergency power to rule Touto. He eventually recovered thanks to Misora's power and immediately exiled Gentoku for his actions while also looking for a way to end the war with the least bloodshed. Despite exiling Gentoku, Taizan still believe there still good in him and vow to return his son back to Touto.

As Namba and Stalk enact their plan to bring humanity to chaos, Taizan is kidnapped by his son and held as a hostage by Stalk to force Sento reviving the original Project Build known as Project Evol, created by his father Shinobu in exchange for Taizan's life. However, it turns out that Gentoku was already planning to save his father, but despite Gentoku aiding the allied Kamen Riders to rescue Taizan and prevent Evolto from obtaining his Evol Driver and Evol-Bottles, the plan backfires, as Evolto retrieved his equipment to transform into Kamen Rider Evol. Taizan becomes the first victim of Evolto, sacrificing his life to save his son from the evil entity's deadly attack. However, this act of sacrifice allows Gentoku to fully revert to his true self, redeeming Gentoku as he finally sides with the other Riders.

After Sento merged his world with that of the "Prime" Kamen Rider universe, an alternate Taizan has been elected as the Prime Minister of Japan as he is shown in a televised address to the public.

Taizan Himuro is portrayed by Meikyo Yamada (山田 明郷, Yamada Meikyō).

Yoshiko Tajimi

Yoshiko Tajimi (多治見 喜子, Tajimi Yoshiko) is the Prime Minister of Hokuto (北都), whose system of governing and political goals are based on social welfare, such as introducing childcare and agricultural programs, putting the needs of its people above all else. But the Skywall Disaster rendered most of the farmland infertile with the resulting economic collapse forcing many citizens to take their children out of school. Her personality revealed to have effected by radiation from the Pandora Box, Tajimi had her government secretly direct most of their funds towards military strength rather than social welfare. After Sōichi and Namba acquired the blueprints of Takumi's Project Build and Touto's guardians in order to manipulate the two other regions' Prime Ministers into waging war and thanks to Gentoku's instigation that the other regions should just try and take the Pandora Box by force, she is the first to declare war against Touto. Her ruthless behavior during the invasion disgusts Kazumi as he threatens her to stop targeting innocent civilians.

During Touto's decisive match against Hokuto, Tajimi acts on Sōichi's advice to station her entire military on Touto's border and invade the country on a contingency order should Grease be defeated. But Tajimi realized too late that she had been manipulated into leaving her nation in a vulnerable position to be taken over by Seito, ending up taken into custody. She is later brainwashed by Evolto's control, transforming her into the Owl Lost Smash (オウルロストスマッシュ, Ōru Rosuto Sumasshu) before being defeated and freed by Kamen Rider Build's Genius Form. This also purified Tajimi's mind as she becomes horrified and remorseful over everything she had done while being the only surviving prime minister. After Sento merged his world with that of the "Prime" Kamen Rider universe, an alternate Tajimi becomes Taizan's Minister of Welfare.

Yoshiko Tajimi is portrayed by Ryoko Gi (魏 涼子, Gi Ryōko).

Masakuni Midō

Masakuni Midō (御堂 正邦, Midō Masakuni) is the Prime Minister of Seito (西都), whose system of governing and political goals are based on economic recovery, doing so by sending its young adults across the world to gather technical knowledge. After Hokuto's war declaration against Touto, expressed an interest in Hokuto Prime Minister Tajimi's offer for alliance, but is ultimately revealed to be an opportunistic manipulator as he stood by sidelines to bide his time. When Hokuto lost the decisive match against Touto, Midō has the Seito military, led by the renegade Gentoku Himuro, invade Hokuto, taking over the defenseless country and bringing Tajimi into their custody. However, Midō is also a nervous man as shown by his reaction during the Touto-Seito proximity match where he begins to stammer whenever it appears that his side was at a disadvantage.

But after losing the fight against Touto, Midō surprisingly proves himself to be honorable in keeping his agreement with Touto while lead to a falling out with Namba that got him killed by Evolto who used his power have Namba assume Midō's identity to use Seito a front for Namba Heavy Industries' operations and his future plots. Following Namba's murder by the alien, Evolto poses as Midō during the final phase of his endgame plan by first placing his kinsmen into governor positions. After Sento merged his world with that of the "Prime" Kamen Rider universe, an alternate Midō becomes Taizan's Minister of Finance.

Masakuni Midō is portrayed by Norimasa Fuke (冨家 規政, Fuke Norimasa).

Evolto

Evolto (エボルト, Eboruto) is the true antagonist of the series and leader of both the Blood Tribe and Faust. A genocidal sociopath, Evolto destroys planets to absorb their energies as a means of gaining power and travelling by using the power of the Pandora Box. After destroying the Martian civilization, he was rendered incorporeal and lost his true physical alien form before being sealed alongside his damaged Evol-Trigger within the Pandora Box by Vernage, who made certain he did not have his Evol Driver to escape his prison from inside.

When a Mars rover arrived for observation, Evolto used it to send a piece of himself to Earth to acquire a host to restore himself. But it backfired when the fragment's attempt of possessing Namba Industries security guard Yuri Banjō resulted in it being assimilated into her unborn child Ryūga. 13 years later, Evolto possessed the astronaut Sōichi Isurugi when he retrieved the Pandora Box from Mars and attempted to destroy Earth, only for Vernage's intervention to result in the Skywall Incident to scatter the Pandora Box across Japan. This forces Evolto to execute a decade-long plan of manipulating various individuals and events for his own gain, such as the foundation of Faust, positioning himself within Namba Heavy Industries and grooming Ryūga as his next vessel. Evolto also used Sōichi's connections to force Shinobu and his son into working for him, tricking a young Misora to purify Fullbottles, and framed Ryūga for Tarō's death while an unconscious Katsuragi was spirited away with his memory and face altered. With Katsuragi's new identity as "Sento Kiryu", Evolto further manipulated him into perfecting the Build System and created other Rider Systems that Katsuragi purposely scrapped. In the hopes of hiding his presence, he feigned his original voice as the default setting of Blood Stalk's system during transformation.

After all Fullbottles were purified, Evolto exposed his treachery to the crews of nascita and his plans to use the Pandora Box to destroy Earth's civilizations, exploiting Namba as they engineered a series of schemes to take over Japan with only Touto and its Kamen Riders as their opposition. After regaining the Evol-Driver, Evolto abandoned his host once regaining his ability to become Kamen Rider Evol (仮面ライダーエボル, Kamen Raidā Eboru) as he transferred himself to Ryūga's body to regain his full power and then into Sento to use his IQ to repair the Evol-Trigger. Once the Evol-Trigger was repaired, Evolto left Sento's body and became a corporeal shape-shifter while assuming Sōichi's appearance. Evolto then proceeded to kill off Namba for serving his purpose when the latter refused to accept being his puppet ruler while winning the maddened Utsumi to his cause. While Vernage revealed that Evolto now gained the power to wipe out the known universe with restored Evol-Trigger while in his final Phase 4 form, Evolto decided to take over Earth instead of destroying it after finding amusement in Namba's final moments and Utsumi's descent into insanity. He is also revealed to be assisted by Shinobu Katsuragi, unaware of the human secretly acting against him. Initially limited to feeling either delight or irritation, Evolto would soon find himself developing human emotions as a result of his Hazard Level increasing each time he is destroyed by Build Genius Form which also causes him to produce Lost Bottles. Evolto also assumed Mido's identity to place his kinsmen in positions of power as governors to execute Build Annihilation Plan but a mutiny by Kengo forced the former into an alliance with his own adversaries.

When later defeated by the four Kamen Riders using a coordinated attack, Evolto, who had just figured out Shinobu's plan to kill him, is forced to impart a fragment of himself within Utsumi to reconstitute himself as a last-minute precaution. He then kills Shinobu while reclaiming his Evol Driver and regaining his full strength, before splitting off a part of himself to possess Kazumi in order to steal back the CD Lost Bottle for the Last Pandora Panel Black (ラストパンドラパネルブラック, Rasuto Pandora Paneru Burakku). He then absorbs the panel to assume his true monstrous form, but was forced back to his Rider Form by the four Kamen Riders and loses a Lost Bottle as well, though he escapes. Combined with his inability to emotionally compose himself, Evolto became so furious by the defeat that he discards his goal of ruling Earth and resume his original plan of wiping out all life on the planet. As the final battle between Evolto and the Riders began, he succeeds in causing Kazumi's death and kills Utsumi after the latter reveals his true allegiance. During the final battle, Evolto becomes omnipotent while killing off Gentoku as he manages critically wound him enough for Ryūga to grab him and sacrifice himself to trap Evolto in the vortex of a wormhole created by the complete Pandora Box. Evolto attempts to cheat death by absorbing Ryūga before Sento manages to save his friend while permanently destroying the alien, before the Pandora Box's effect of creating a new world by merging Build's world with the "Prime" Kamen Rider universe completely renders all traces of Evolto's essence non-existent.

A cruel and ruthless character, Evolto committed several heinous acts using Sōichi's body as a vessel, killing without hesitation and even turned a child into a Smash on one occasion, with his plots and actions resulting in several deaths. Evolto is a very patient manipulator, having spent years establishing his plans while easily winning allies or placing enemies in situations that play to his advantage but can be taken off guard by unexpected occurrences where he was forced to improvise in order to survive. Due to the successful nature of his plots in the first half of the series, Evolto becomes arrogant and overconfident which quickly proves to be a liability, as his reliance on luck backfired several times. It also extends to his tendency of toying with his opponents as he fails to expect a stronger counterattack, which proves costly when the Riders were able to force him out of his true form just moments after he had regained it, all because he chose to gloat rather than killing them when he had the chance. Another flaw Evolto suffered was his inability to handle human emotions as the result of having used host bodies and his exposure to Build, making him more prone to blind rage and later expressing sheer fear in the penultimate episode when sucked into the wormhole and then at his impending doom after realizing that he would not survive Sento's final attack.

As Kamen Rider Evol, Evolto uses the Evol Driver (エボルドライバー, Eboru Doraibā) and Evol-Bottles (エボルボトル, Eboru Botoru) which the Build System was reversed engineered from. As a Rider, Evol has a high-speed movements that go on par with any previous Kamen Riders who has this ability, with Build Genius Form is the only one who can match Evol's acceleration powers in their home universe. Evol's finishing move is the Evoltic Finish (エボルテックフィニッシュ, Eborutekku Finisshu). Each of his forms are treated as evolution of his Phases (フェーズ, Fēzu):

• Cobra Form (コブラフォーム, Kobura Fōmu): The primary form of Evol, known as "Phase 1" (フェーズ1, Fēzu Wan) and accessed with the use of Cobra Evol-Bottle. Evol is capable of secreting enhanced poisons and is able to outmaneuver his opponents with blinding speed.
• Dragon Form (ドラゴンフォーム, Doragon Fōmu): Also known as "Phase 2" (フェーズ2, Fēzu Tsū), it was accessed when Evol possessed Ryūga and created the corresponding Dragon Evol-Bottle from his body. Aside from adding Cross-Z's Beat Closer to his arsenal, Evol can also initiate pyrokinesis. This form was lost after Ryūga stole the Dragon Evol-Bottle and used it to transform into Great Cross-Z.
• Rabbit Form (ラビットフォーム, Rabitto Fōmu): Also known as "Phase 3" (フェーズ3, Fēzu Surī), it was accessed when Evol possessed Sento and created the corresponding Rabbit Evol-Bottle from his body. The result of both Sento's gambit in raising his Hazard Level to 6 and self-destruction with a Pandora Panel concluded in his possession and the change of his hair color to white. In addition to Build's Drill Crusher, Evol gains a sharp increase in acceleration and superhuman agility.
• Black Hole Form (ブラックホールフォーム, Burakku Hōru Fōmu): Kamen Rider Evol's true form, also known as "Phase 4: Perfection" (フェーズ4: 完全体, Fēzu Fō: Kanzen-tai) and accessed through the use of Cobra Evol-Bottle and the Evol-Trigger (エボルトリガー, Eboru Torigā). This form was previously sealed by Vernage during their battle on Mars, until the energies from the combined attack of Cross-Z Magma, Grease and Rogue were exploited to restore the Evol-Trigger, restoring his corporeal form. Incredibly powerful, Evol can even manipulate black holes and destroy celestial bodies. Before his arrival on Earth, Evol had once brandished an energy blade in a fight against Vernage.

As the Rider (ライダー, Raidā) Evol-Bottle invokes every transformation, it can also utilize Creation (クリエーション, Kuriēshon) when in conjunction with a normal Fullbottle.

• Kikanhou (機関砲, Kikanhō, Autocannon): By inserting the Gatling Gun Fullbottle, Evol summons the Hawk Gatlinger and can perform the Kikanhou Finish (機関砲フィニッシュ, Kikanhō Finisshu).

By activating Evol-Trigger's Feverflow (フィーバーフロー, Fībāfurō) Mode while obtaining all 10 Lost Fullbottles stacked in the black Lost Panel merged with himself, Evolto gained the ability to assume his true Monstrous Form (怪人態, Kaijin-tai). His signature ability is Black Hole Break (ブラックホールブレイク, Burakku Hōru Bureiku), which allows him to assimilate celestial bodies as he consumed the moon and part of Earth to assume his Ultimate Form (究極態, Kyūkyoku-tai) with access to Evolti Voider (エボルティヴォイダー, Eboruti Voidā) shoulder units and Evolti Grasper (エボルティグラスパー, Eboruti Gurasupā) gauntlets. But while it is Evolto's strongest form, the Evol-Trigger becomes his own weakpoint as Gentoku dies removing it to give Build and Cross-Z their chance to destroy the alien.

Evolto is voiced by Tetsuo Kanao (金尾 哲夫, Kanao Tetsuo). While possessing Sōichi Isurugi and later assuming his likeness, he is played by Yasuyuki Maekawa.

Kengo Inō

Kengo Inō (伊能 賢剛, Inō Kengo) is Evolto's second-in-command who served as advisor to Seito Prime Minister Midō before being arranged to become new governor of Touto by the events of Kamen Rider Build the Movie: Be the One, seeking to carry out the Blood Tribe's initial plan to destroy Earth after the Japanese civil war Evolto caused had ended. As part Build Annihilation Plan, Inō brainwashed most of the Japanese population in against Sento, including Ryūga whom he made into his personal agent. Ino eventually faces Sento personally as Kamen Rider Blood and at first, managed to dominate against Genius Form, before eventually being defeated by the fusion form of Sento and Ryuga, Kamen Rider CrossZBuild.

Possessing the Cobra Lost Bottle, Inō uses it with Ryūga's Build Driver and Great Cross-Z Dragon, combined with Sento's Hazard Trigger to transform into Kamen Rider Blood (仮面ライダーブラッド, Kamen Raidā Buraddo).

Kengo Inō is portrayed by Masanobu Katsumura (勝村 政信, Katsumura Masanobu).

Mitsuomi Gōbara

Mitsuomi Gōbara (郷原 光臣, Gōbara Mitsuomi) is a member of Blood Tribe and a former advisor to Hokuto Prime Minister Tajimi who poses as the new governor of Seito. He can transform into Zebra Lost Smash (ゼブラロストスマッシュ, Zebura Rosuto Sumasshu) using the Shimauma (シマウマ, Zebra) Lost Bottle. He was defeated by Kamen Rider Grease after initially defeating him in their first encounter.

Mitsuomi Gōbara is portrayed by Takashi Fujii (藤井 隆, Fujii Takashi).

Ryōka Saiga

Ryōka Saiga (才賀 涼香, Saiga Ryōka) is a female member of Blood Tribe and a former aide to Touto Prime Minister Himuro who poses as the new governor of Hokuto. She can transform into Scissors Lost Smash (シザーズロストスマッシュ, Shizāzu Rosuto Sumasshu) using the Hasami (ハサミ, Scissors) Lost Bottle. She is defeated by Kamen Rider Rogue after initially defeating him in their first encounter.

Ryōka Saiga is portrayed by Rena Matsui (松井 玲奈, Matsui Rena).

Killbas

Killbas (キルバス, Kirubasu) is the older brother of Evolto, and the main antagonist of Build New World: Kamen Rider Cross-Z. Killbas is disguised as a famous dancer named Satoshi Kakizaki (柿崎 悟志, Kakizaki Satoshi).

By possessing the Build Driver and a yet identified transformation item, Killbas transforms into Kamen Rider Killbas (仮面ライダーキルバス, Kamen Raidā Kirubasu).

Killbas is voiced by Anri Katsu (勝 杏里, Katsu Anri), while his human disguise is portrayed by Gaku Shindo (進藤 学, Shindo Gaku).

Clone Smash

The Clone Smash (クローンスマッシュ, Kurōn Sumasshu), unlike regular Smash, are artificially created monsters created from pure Nebula Gas. Being enhanced versions of the Press, Stretch, Strong and Flying Smash Hazard, while acting an impulse to attack until being destroyed, the Clone Smash are stronger and durable due to their inability to feel pain that allow them to withstand most attacks that destroyed previous Smash types. The Clone Smash are later used as materials to power a Lost Bottle to enable its user's transformation into a Lost Smash.

Lost Smash

Lost Smash (ロストスマッシュ, Rosuto Sumasshu) are Smash breeds created by Evolto and Katsuragi as the final Smash evolution. The experiment includes a human victim being heavily dosed with Nebula Gas and transforms into the Lost Smash by absorbing a pair of nearby Clone Smash. Aside from heightened aggression and being easy to manipulate, they are also bound to die should they be defeated. The Genius Fullbottle of Kamen Rider Build has the ability to save these victims and therefore to remove traces of Nebula Gas.

The Lost Bottles (ロストボトル, Rosuto Botoru) created by Shinobu Katsuragi were used to invoke the target's transformation into Lost Smash. In truth, their actual purpose is to complete the Lost Panel of Pandora Box to take control of humanity. The full set of Lost Bottles work differently depending on the Pandora Panels they slotted into: the Last Pandora Panel Black allows Evolto to regain his monstrous form by absorbing it whereas its White counterpart can merge with five other Pandora Panels to fuse Earth with its alternate counterpart, therefore averting the Skywall Disaster.