Taiyo Koga was born on 28 October 1998 in Chiba. He came through Kashiwa Reysol's youth ranks and went on loan to Avispa Fukuoka in 2018 before returning to Kashiwa permanently in January 2019. He has remained a one-club centre-back since.
His Kashiwa career has been remarkably consistent. The 2023 season produced 33 J1 League matches with an assist, 2024 brought 37 J1 matches with a goal, and 2025 produced 38 J1 League matches as Kashiwa's senior centre-back.
For Japan, Koga was a member of the squad that won the EAFF E-1 Football Championship in 2025, playing 2 tournament matches.
A 182cm two-footed centre-back with composure, ball-playing security and the leadership of a long-serving Kashiwa starter, Koga is one of the J1 League's most reliable senior centre-backs. He is a candidate for the wider 2026 FIFA World Cup squad as a senior CB option.