Yagi is the manager of the Kamogawa Gym and a contemporary of Miyata's father. His duties primarily consist of publicity and match booking, but he also takes part in managing the finances, selling merchandise, and occasionally even assists with the training now and then. He is a kind and friendly person, often adding ~kun to the end of the names of the Kamogawa gym members.

He is a master fisherman and whenever he fishes his personality changes (in the words of Miyata's father, "he gets the face of a demon"). He is so good in fact, that it has been said that he could become the World Champion of fishing. Additionaly, numerous fishing ponds put up "No Yagi Allowed" signs after losing so many customers because Yagi was catching all the fish.