Koki Niwa

Niwa had a prolific junior career beginning in 2008. He reached the quarter-finals at the 2008 India Junior Open in Pune, India, and won the doubles title with his partner Yuki Hirano. At the 2008 World Junior Championships in Madrid, Spain, he parterned with Kenta Matsudaira to reach the semi-finals. The following year, Niwa partnered with Asuka Machi to win the 2009 ITTF Cadet Challenge and ITTF Junior Circuit Finals in Tokyo, Japan.

At the 2009 World Junior Table Tennis Championships, Niwa reached the quarterfinals in the men's singles event before being defeated by Lin Gaoyuan. Niwa qualified for the 2009 World Table Tennis Championships in Yokohama, Japan by defeating Josef Simoncik in the qualification tournament. Niwa reached the round of 64 before being defeated by Germany's Dimitrij Ovtcharov.

At the 2010 Singapore Youth Olympics, he won a gold medal in the Boy's Singles Event, and a gold medal partnering Ayuka Tanioka in the Mixed team event. Niwa won the U21 title at the 2011 Dortmund Pro Tour German Open by defeating Kim Min-seok. At the 2011 Incheon Pro Tour Korea Open, he defeated Jeoung Youngsik to obtain his second U21 title that year. At the 2011 Manama World Junior Table Tennis Championships, he won the gold medal in the men's singles event, defeating Lin Gaoyuan of China.

By 2012, the 17 year old world junior champion was gaining widespread attention. His breakthrough came at the 2012 Asian Olympic Qualification Tournament where he overcame world ranked No. 1 Ma Long and became the inaugural Asian player in the sport to qualify for the Olympics.[7] Partnering with Kenta Matsudaira, Niwa overcame the Chinese pair of Wang Hao and Zhou Yu to win the 2012 World Tour Polish Open doubles title.

Niwa qualified for the 2013 World Table Tennis Championships seeded 15.[8] He reached the fourth round in the men's singles event before being defeated by Ma Long. He partnered Kenta Matsudaira in the doubles event and reached the third round before losing to compatriots Jun Mizutani and Seiya Kishikawa. At the 2013 World Tour Japan Open in Yokohama, the Niwa/Matsudaira pair lost in the finals against compatriots Jin Ueda and Maharu Yoshimura.

At the 2014 World Team Table Tennis Championships in Tokyo, Niwa won 4 out of his 5 matches, contributing to Team Japan's bronze medal. At the 2014 World Tour Grand Finals in Bangkok, the Niwa/Matsudaira pair lost in the final to Korean pair Cho Eonrae and Seo Hyundeok. Niwa won the 2014 World Tour Russian Open title in the men's singles event, defeating England's Paul Drinkhall in the final. The Niwa/Matsudaira pair competed in the semi-finals and were defeated by the Russian pair Fedor Kuzmin and Grigory Vlasov.

At the 2015 World Table Tennis Championships, Niwa reached the 4th round before being defeated by China's Fan Zhendong. In the doubles event, the Niwa/Matsudaira pair reached the semi-finals, and were defeated by Fan Zhendong and Zhou Yu. This was the last international partnership with Kenta Matsudaira.

At the 2016 World Team Table Tennis Championships in Kuala Lampur, Niwa contributed to Team Japan's success in winning the silver medal. The team lost to Team China in the final. Niwa represented Japan at the 2016 Summer Olympics in the men's singles event. He reached the quarterfinals before being defeated by eventual silver medalist Zhang Jike. In the Men's team event, Niwa contributed to team Japan's first silver medal in the category. However, Niwa expressed discontentment with his performance, not winning any singles matches.[9]

Niwa began the year by winning a bronze medal at the 2017 ITTF Asian Championships in Wuxi, China. In the quarterfinals, he defeated world ranked #3 Xu Xin, but lost to Korea's Jeong Sangeun in the semi-finals. At the 2017 World Table Tennis Championships, Niwa partnered with Maharu Yoshimura to win the bronze medal. The Niwa/Yoshimura pair reached the semi-finals where they lost to Chinese pairing and eventual champions Fan Zhendong and Xu Xin in the men's singles event, he reached the quarter finals, defeating Dimitrij Ovtcharov in the fourth round, and losing to Fan Zhendong in the quarterfinals. At the 2017 World Tour Japan Open, the Niwa/Yoshimura pair reached the finals of the men's doubles event where they lost to the Chinese pairing of Ma Long and Xu Xin.

Niwa and Kenta Matsudaira were doubles partners from 2008 to 2015. Their playstyle is characterized by both players' unorthodox playstyles, with Niwa frequently incorporating "chiquita" banana flicks and Matsudaira frequently using his tomahawk service. Both players frequently use their backhand to win points.

The pair first competed in the international scene at the 2008 Cetniewo Polish Youth Open. In 2012, they defeated the Chinese pairing of Wang/Zhou to secure their first men's doubles titles in the ITTF world tour scene. The pair won a bronze medal at the 2015 World Table Tennis Championships. Niwa and Matsudaira have not partnered on the international scene since 2015.

Niwa and Maharu Yoshimura have been frequent doubles partners starting in 2016. The pairing first rose to prominence at the 2016 Summer Olympics Men's Team Event where the pair contributed to Japan's silver medal. At the 2017 Asian Championships in Wuxi, the pair reached the semifinals before losing to Fan Zhendong/Lin Gaoyuan. At the 2017 World Table Tennis Championships Men's Doubles event, the pair won a joint bronze medal. The following month, at the 2017 World Tour Japan Open, Niwa/Yoshimura reached the finals before losing to Ma Long/Xu Xin in three straight games.

Niwa and Chen have met 9 times in the international scene, with Niwa leading 5--4. Their first encounter was at the 2009 Harmony China Open where Niwa won 4 games to 1. They met another two times at the 2011 Harmony China Open where Chen defeated Niwa in the U21 Men's singles final, and Niwa defeated Chen in the Men's singles main bracket. In their most recent encounter, Chen won 4 games to 2 over Niwa at the 2017 Asian Cup main tournament bracket, and Niwa won 3 games to 0 in the group stage.

Niwa and Kim have met 10 times with Niwa leading 6--4. Their first encounter was at the 2009 Korea Open U21 Men's singles event where Niwa won in full games. Niwa and Kim have met 3 times in the semi-final stages of U21 pro tour events. At the 2011 Pro Tour Germany Open U21 Men's singles final, Niwa won in full games over Kim. Their most recent encounter was in 2015 where Niwa won 4 games to 1 at the 2015 World Tour China Open.

Niwa and Lin Gaoyuan have met 5 times with Lin leading 3--2. In their first encounter, Lin won in full games at the 2009 World Junior Table Tennis Championships. At the 2011 World Junior Table Tennis Championships, Niwa took revenge against Lin and won 4 games to 2 to win the tournament. The 2017 Seamaster World Tour Platinum Austria Open marked the first time in 6 years that the two had met. Lin won 4 games to 1 over Niwa.

(W) Won; (F) finalist; (SF) semifinalist; (QF) quarterfinalist; (#R) rounds 4, 3, 2, 1; (RR) round-robin stage; (S) Singles Tournament; (D) Doubles Tournament; (MD) Mixed Doubles Tournament; (T) Team Tournament.