is a Japanese badminton player who specializes in doubles. He plays for the BIPROGY badminton team and is a member of the Japanese national team. Kumagai won his first BWF World Tour title at the 2025 Kaohsiung Masters.
Kumagai began playing badminton at the Sendai Yamato Junior club before attending . In 2018, he partnered with Yoshifumi Fujisawa to win the boys' doubles title at the .
The following year, Kumagai represented Japan at the 2019 World Junior Championships, winning a bronze medal in the mixed team event. In the individual mixed doubles event, he and partner Mizuki Otake reached the quarterfinals, where they were defeated by the Chinese pair Jiang Zhenbang and Li Yijing in three games match (20âÂÂ22, 21âÂÂ18, 21âÂÂ23).
Kumagai studied sport science at Nihon University. Partnering with Kota Ogawa, he won the men's doubles title at the . Consequently selected for the Japanese national B team, the pair made their World Tour debut at the 2023 Indonesia Masters I Super 100, finishing as runners-up.
After graduating from university in April, Kumagai joined the badminton team. He formed a men's doubles partnership with Hiroki Nishi, training under former national players Hiroyuki Endo and Kenichi Hayakawa. In their debut season, the pair finished as runners-up at the Super 100 Odisha Masters and the Kazakhstan International. Domestically, at the All Japan Corporate Team Championships, Kumagai partnered with Yuta Watanabe to defeat the former world No. 1 pair, Takuro Hoki and Yugo Kobayashi, in the final. This victory secured the team title and earned the pair the Men's MVP award.
Kumagai and Nishi claimed their first international title as a pair at the Northern Marianas Open in August, defeating compatriots Haruki Kawabe and Kenta Matsukawa in the final. They subsequently won their first World Tour title at the Super 100 Kaohsiung Masters. The pair also finished as runners-up at the Super 100 Indonesia Masters I and reached the quarterfinals of two Super 500 tournaments: the Japan Masters and the Australian Open. Following these results, they reached a career-high world ranking of No. 32 in November.
Kumagai and Nishi opened the season by making their Super 1000 debut at the Malaysia Open. The pair advanced to the second round, where they were defeated by their compatriots Takuro Hoki and Yugo Kobayashi. He was part of the Japanese team that won Japan's first men's team title at the Asia Team Championships. In the final against China, Kumagai and Nishi defeated He Jiting and Ren Xiangyu in three games to help secure the victory. Kumagai achieved a career-high world ranking of 26 on 10 March.
The BWF World Tour, which was introduced on 19 March 2017 and was held in 2018, is a series of elite badminton tournaments sanctioned by the Badminton World Federation (BWF). The BWF World Tours are divided into levels of World Tour Finals, Super 1000, Super 750, Super 500, Super 300, and the BWF Tour Super 100.
Men's doubles
Men's doubles
Record against year-end Finals finalists, World Championships semi-finalists, and Olympic quarter-finalists. Accurate as of 8 January 2026.