Ojī (お爺) is the coach for the Rokkaku Boys Tennis Club.
According to Echizen Nanjirō, this fragile-looking old man has been coaching Rokkaku even before his days at Seigaku. He used to make wooden rackets for a living and are responsible for all the rackets that the team currently uses. Until this year's match against Seigaku, his products have never suffered any scratch. During Rokkaku's first round match at the Nationals, Higa's Kai Yūjirō deliberately aimed a shot at Ojii, knocking him unconscious. He had to be carried off on a stretcher. Fortunately, Rokkaku later reported that the old man was fine. During the Seigaku-Rokkaku joint training camp, Ojī also changed the grip tape on Echizen Ryoma's racket to give his hand a better fit.