[3] He moved up to the U-18s in 2020 and was part of the team that were beaten finalists in the U-18 Japan Club Youth Championship, losing 3–2 to Sagan Tosu U-18s, although Tawaratsumida himself only made a series of late cameos throughout the competition.
[8] On 23 February 2023, he made his debut in a J1 League match against Kashiwa Reysol where he appeared as an 80th-minute substitite for Koki Tsukagawa.
[9][10] In matchweek 4 of the 2023 season, Tawaratsumida was named in the starting XI for the first time in a 3–1 win over Yokohama FC and made an impact with his ability to dribble into the opponent's box.
[11] His dribbling ability was on display in October, when Tawaratsumida won the J1 League Goal of the Month award for his solo effort in a 3–0 win over Gamba Osaka.
[12] At the end of his debut season, Tawaratsumida played 35 games for FC Tokyo in all competitions, scoring two goals.