Yagi Haruhiko (八木 晴彦) is the boxing manager of the Kamogawa Boxing Gym. 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.