Koki Kumasaka

is a Japanese footballer who plays as a defensive midfielder for Kashiwa Reysol.

Club career University football Enrolled at the Tokyo International University, he helped his side to second place in the Kanto University Division 1 League. With four goals and two assists, he was named in the best XI for the league. He made his professional debut in Reysol's 1–1 J1 League draw against Albirex Niigata on 30 March 2024, and went on to appear in the next three matches. An injury during the Chibagin Cup limited his playing time, and his debut season was not seen as successful.

After ten league appearances in 2024, Kumasaka remained in the first team the following season, featuring in Reysol's pre-season preparation before playing ninety minutes in their opening J1 League fixture against Avispa Fukuoka. Following the appointment of Spanish manager Ricardo Rodríguez in February 2025, Kumasaka began to feature a lot more in the Kashiwa Reysol first team, forming a partnership with Riki Harakawa. In March of the same year, he changed his contract type from Pro C to Pro A, having played 450 minutes in the J1 League.

International career Without having previously represented Japan at youth international level, he was called up to the senior squad in May 2025.

Style of play A volante, Kumasaka is noted for his ability in one-on-one duels, as well as his agility despite his height, standing at 1.85 metres.

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