Ryuhei Aoi is a coach at Southern Tennis Club and primarily assists Eiichirou Maruo on his journey to become a professional. He is a ex-professional tennis player who retired after receiving an injury.

Ryuhei has a calm personality and likes players to take it easy while working hard. He advices Eiichirou to depend on his instincts and knowledge both or he will lose all his skill and end up being weak. He also cares for his students and when stopped Eichirou when he tried fast serve without any prior training.

(Source: Baby Steps Wikia)