13 Sentinels: Aegis Rim

13 Sentinels is primarily set during a fictionalised version of the 1980s in the Shōwa period, but also jumps between Japan during the later years of World War II and the distant future.[8][9][10] The story follows its thirteen protagonists, all of high school age, as they are dragged from their normal lives into a fantastical war against invading alien forces using the Sentinel mechas.[2] The storyline is split between multiple characters, and by following each character the player aims to avert a disastrous future for mankind.[1]

The scenario follows the perspective of thirteen different characters. While several characters are native to the 1980s, several come from either the future or the era of World War II.[10] They are Juro Kurabe, an otaku who accidentally summons a Sentinel; Iori Fuyusaka, an outgoing student troubled by strange dreams; Ei Sekigahara, an amnesiac young man pursued by a mysterious organisation; Keitaro Miura, a young man from World War II-era Japan; Takatoshi Hijiyama, Miura's underclassman from the same time period; Nenji Ogata, a good-hearted delinquent; Natsuno Minami, a track team member fascinated by the occult and UFOs who ends up travelling between time periods; Shuu Amiguchi, a playboy delinquent with a kind heart; Yuki Takamiya, a notorious sukeban (delinquent girl) and childhood friend of Natsuno; Tomi Kisaragi, a girl from the near-future sent into the 1980s; Megumi Yakushiji, a girl from the near-future obsessed with Juro; Ryouko Shinonome, a sickly girl tasked with pursuing an escaped prisoner dubbed "426"; and Renya Gouto, who leads the Sentinel pilots.[8][9][10][11]

There are several notable supporting characters. Morimura is both the teacher for Juro and Fuyusaka's class and the school nurse. Tsukasa Okino is a genius student with deep knowledge of the Sentinels, disguising himself as a girl in the 1940s to learn about the time period. Chihiro is a mysterious girl; sporting an implanted personality, she accompanies Renya. Kyuuta Shiba is an apparent friend of Juro, but possesses strange powers and a hidden agenda. Erika Aiba is a student who tags along with Takamiya as they solve mysteries surrounding the Sentinels. Tetsuya Ida, while ostensibly a part-time instructor, is the chairman of the covert Special Intelligence Agency. The small robot BJ accompanies Natsuo on her journeys through time. Shippo appears as a talking cat, striking a deal with Megumi to "save" Juro.[7][10][12]

Kamitani's original concept had seven or eight characters, but as the first artwork for the concept was published in 2013, he decided to increase the number to thirteen; this exponentially increased the company's workload.[15] Prior to incorporating mechas, the story revolved around young people with superpowers inspired by the TV drama series Night Head. Due to lacking excitement and overt science fiction elements, he rewrote the premise. Kamitani based the narrative on the original video animation Megazone 23. He was originally planning on basing the narrative of Two Years' Vacation by Jules Verne, and the characters Renya and Megumi being based on the novel characters Gordon and Cross.[16] In contrast to his work on Odin Sphere, where he had created the overall story while other writers worked on the game scenario, Kamitani wrote the entire scenario of the game himself both in and out of office hours over the course of three years. Kamitani chose to set the game in 1980s Japan due to his own experience; his knowledge of the modern Japanese school system was limited, and the lack of mobile phones in that era allowed for more face-to-face conversations between characters in-game.[15]

Kamitani, who previously handed character designs himself in previous games, handed duties to Hirai and Kida due to the workload.[15] The character design was influenced by the work of mangaka Akira Kagami, a favorite of Kamitani in his youth. Hirai was given the stylistic direction of "girls and robots" for the character designs.[16] Unlike past Vanillaware games like Odin Sphere and Muramasa, which repeatedly used the same 2D background environments for their event scenes, the team created different backgrounds for several event scenes for the game and experimented with using some 3D assets for objects for additional layering in scenes, increasing development time. The added depth also created problems for the team with conveying emotions during cutscenes.[15] During production, the character designs of Ryouko and Megumi were switched to better fit their emerging story personalities.[16]

The team's aim was to push the boundaries they had previously established for 2D artwork in video games.[13] The adventure segments were designed to express the classic style of adventure games with a more intuitive interface design and response, for which the Cloud Sync system was designed. Though Kamitani thought the Cloud Sync system would be simple, its implementation proved extra challenging. The real-time strategy elements were based on Vanillaware's earlier effort GrimGrimoire, with the balance of adventure and battle sections in 13 Sentinels being based on original plans for GrimGrimoire. As the StarCraft-based gameplay of GrimGrimoire had met with a mixed response in Japan, Kamitani combined it with elements of the tower defense genre popular in the region. These elements were mostly handled by the programming team, led by Kentaro Ohnishi. The Archive was suggested by staff member Kouichi Maenou as a means for players to explore the game's mysteries. This aspect was handled by other staff, as Kamitani was in the middle of scenario writing. He reminisced that due to the various development challenges and his own workload, he felt like an absentee compared to the other staff as there was comparatively little interaction during development. The increased workload, scope, and challenges for the game's development led to significant changes in the studio's usual development cycle.[15]

The music and sound design for the game were handled by Basiscape, a music company led by Hitoshi Sakimoto who had collaborated on other Vanillaware projects.[3] The music was composed by a team led by Sakimoto, and included Yukinori Kikuchi, Mitsuhiro Kaneda, Yoshimi Kudo, and Rikako Watanabe.[17] Sakimoto was contacted by Kamitani at the beginning of development when the New Year image was designed. The first track composed was the opening theme "Brat Overflow", which featured in the reveal trailer and would inform the game's musical style from that point on. Compared to his earlier work with Vanillaware, Sakimoto worked more on keeping a unified musical image. The music was themed around techno, but the team worked to keep melodic balance in the score. Its theme was "juvenile", with Sakimoto needing to redo his early work with Kamitani's help.[18] The game featured a vocal theme, "Seaside Vacation", performed by singer Hu Ito who was the singing voice for in-game idol Miyuki Inaba.[19] In keeping with the main setting, the song's style was based on Showa-era pop songs, though there were no particular inspirations behind the song and singer. The lyrics were written by Watanabe.[18] A soundtrack album is set for release on February 27, 2020, the physical version being exclusive to Atlus's online store. The album features four discs, and has a cover art drawn by Hirai. The album will also be released digitally worldwide through iTunes.[20][21]