Although he played as a regular player, he lost his place due to an injury in 2010.

After playing for two seasons, he moved to his local club Avispa Fukuoka in 2012.

In August 1995, Koga was selected by the Japan U-17 national team for the 1995 U-17 World Championship and he played full time in all three matches.

In June 1997, he was also selected by the Japan U-20 national team for the 1997 World Youth Championship, but he did not play in any matches.

This biographical article related to a Japanese association football defender born in the 1970s is a stub.