Sadaharu Inui (乾貞治 Inui Sadaharu) is a 3rd-year student and regular member of the Seigaku tennis team. He is an intelligent player and is best known for collecting player data, which he incorporates into a unique playing style known as "Data Tennis". During his match against Tezuka in the manga, it is hinted that he is the 3rd strongest 3rd year in Seigaku, behind Tezuka and Fuji.