I remember that when he was with Akroma, his flag was Japan.
He is supposed to be a half-Japanese, half-French dual citizen, so it should have been fine to keep the Japanese flag originally. But why?
I'm a dual French-Japan citizen, born and living in France. JP doesn't allow dual citizenship, but France does. At 20, Japan required me to chose if I want to keep my JP citizenship or my FR citizenship. If I have chosen FR, I would have been stripped of my JP citizenship, while if I choose JP, (which I did) I can keep both because France can't strip me of my citizenship. De jure, I'm only Japanese for the Japanese gov but de facto, I'm a dual citizen.