Kazuya Maruo is Eiichiro's father. He is the one who first accepted Eiichirou Maruo's plan to become a professional tennis player after hearing his proposal. Eiichirou's father has a somewhat mild personality. He was ready to give Eiichirou a chance to become professional in tennis. Later on, he was ready to help E-chan in anything he wants for his tennis training, claiming that until the All Japan tournament, he will provide any help he wants since Ecchirou wants to become one with his own will and is willing to work hard for it. However, since Eiichirou said that he would give up on being a professional tennis player if he did not win the tournament, He plans to make Ecchirou keep that promise.