Mitoma professed to feeling unprepared to enter professional football at age 18, citing the struggles of fellow Kawasaki academy products Ko Itakura and Koji Miyoshi to win regular playing time with the senior squad.

Playing in the Kanto University Soccer League [ja] with Tsukuba, he was named to the all-league XI in his final three seasons while majoring in physical education.

In addition, Tsukuba appeared in the 2016 and 2017 Emperor's Cup tournaments making an upstart run to the round of 16 in the latter edition, upsetting J.League clubs YSCC Yokohama, Vegalta Sendai (against whom Mitoma scored a brace), and Avispa Fukuoka along the way.

While enrolled in college, Mitoma also occasionally joined Frontale's senior team for training sessions as a Special Designated Player starting in his sophomore year, appearing in a single J.League Cup match in 2019.

[13] On 13 August 2022, Mitoma made his Premier League debut for Brighton, coming on as a 75th-minute substitute for Leandro Trossard in a goalless draw against Newcastle United at the Falmer Stadium.

[14] He made his first start for Albion on 24 August, playing 67 minutes of the 3–0 away victory League One side Forest Green Rovers in the EFL Cup second round.

[28] After being capped at youth level, Mitoma was called up to the Japan senior squad for the first time in November 2021 for 2022 World Cup qualifiers against Oman.

[33][34] The photographer Petr David Josek revealed that a total of four agencies — AP, Reuters, AFP and Getty Images —[34] were approved to enter the suspended catwalk to take bird's eye photos, but the latter three missed the shot because they were at the opposite side of the pitch anticipating a Spanish goal instead.

[33][34] Mitoma is the childhood friend of fellow Japan international and former Kawasaki Frontale teammate Ao Tanaka, who currently plays for Championship club Leeds United.