Kosei Tanaka has two losses against two opponents on his boxing record. For a list of Tanaka's best fights, refer to "Best fights of Kosei Tanaka".
On October 14, 2024 Kosei Tanaka met Phumelele Cafu in a super-flyweight (WBO) world-title defense fight. Tanaka was 29 years old and with a record of 20-2 (11), and Cafu was 20 years old and with a record of 10-0-3 (8). Tanaka lost the fight via 12-round split decision and lost the title.
On December 31, 2020 Kosei Tanaka fought Kazuto Ioka in a super-flyweight world-title fight for Ioka's WBO title. Tanaka was 25 years old and with a record of 15-1 (9), and Ioka was 31 years old and with a record of 25-2 (14). Tanaka lost the fight via 8th-round TKO.
