Koga is about 169 cm. He has medium length grey hair with some wrinkles on his forehead. He wears circular stainless steel glasses and his eyes are usually closed.
Koga is the oldest among all coaches in this series. He is 71 years old and has been Kitasumi High’s instructor for a while. Koga is a strategist who can instantly determine the player’s habits and weaknesses. However, due to his age, he can make some wrong judgments. As at the beginning of the practice match against Kuzuryu High, Koga underestimated Sora’s team, as he instructed his players not to wear their club’s uniform. Believing that Kuzu-High was not taking this game seriously as they wore their team’s practice jerseys. When Kenji and Sora scored a couple of points for their team, Koga apologized to his players and instructed them to change back into their official uniforms as their team’s full strength will play this game.
He is very kind and also advises players of other teams. When Kitasumi High won their practice match, Koga approached Kurumatani and gave him some guidance. He informed Sora, if he had kept his cool and drawn a foul during the last play or passed the ball to Kenji, Kuzuryu High would have won the match.
Previously, Koga had thought of retiring as the team’s instructor. Ever since Taro got enrolled in Kitasumi High, their club has gained some recognition. Koga believes that Taro is the one who can help their team to qualify for the Inter-High tournament and decided that he will retire when Taro’s last Inter-High chance ends.
- The name Koga means "antiquity" (古) (ko) and "delighted" (賀) (ga).
- “What’s this… They’re not wearing uniforms. Ah you guys don’t have to wear uniforms. We’ll look lame if we’re the only one’s taking it seriously.” – to Kitasumi High (Chapter 38)
- “We’ll Tarou said he will quit if we didn’t accept the practice match with Kuzuryu High.” – to Kitasumi High (Chapter 38)
- “You guys… Properly put on your uniforms. All starting members come out at once. Redo your warm ups this time. This game will be played with our full power.” – to Kitasumi High (Chapter 38)
- “It’s true that it was a bad shot… But the failure was before that. You hesitated whether to shoot or pass right? Tarou was right behind you with 4 seconds left you had more than enough time to even include a fake. If you had thought it through you could have even gotten a foul out of it.” – to Sora Kurumatani (Chapter 55)
- “And that’s where your biggest mistake was… The moment you got the ball you weren’t looking at the goal. As soon as you got the ball from number 7 (Chiaki) you were looking at number 9 (Kenji) and you were probably thinking a draw is the best we can do… Changing your position kind of backfired you there.” – to Sora Kurumatani (Chapter 55)
- “Let’s play again sometime. I have enjoyed it.” – to Sora Kurumatani (Chapter 55)