After graduating from junior high school, Koga embarked on a career which took him first to English Premier League side Leicester City.
[3] Having failed to establish himself in the club's youth ranks, he moved to the Netherlands, signing with PEC Zwolle, where he stayed for two years.
[7] Having only made one appearance for Renofa Yamaguchi, he dropped down to the Japan Football League with FC Kariya for the 2021 season.
[8] After a short spell in Australia with Caroline Springs, Koga signed for J3 League side YSCC Yokohama for the 2022 season.
This biographical article related to a Japanese association football forward, born in the 1990s is a stub.