Sadaharu Inui

The brain behind Seigaku's team. He takes data for all the games, including personal data for his rivals along with teammates. He's formerly known as Seigaku number 3 (right behind Fuji and Tezuka) - the data tennis man. But due to losing the Seigaku's regular selection matches in the beginning of the series (mostly because of Ryoma's appearance), he played Seigaku's manager for the first 50 or so episodes.