Tanaka "Susan" Fumiko is the alias adopted by Nobuyuki Sakakibara, principal of Wakame High School. He assumes this identity by concealing his face behind a red ski mask, hiding his true appearance from Masaru Hananakajima and the Sexy Commando Club. This transformation originated from a pivotal past event: as a teacher, Sakakibara expended all his physical energy to push the entire school building four inches off its foundation. This extreme feat visibly aged him but succeeded in motivating a previously lazy student who later became Japan's Prime Minister.

Prior to becoming principal, Sakakibara won six consecutive championships as a Sexy Mate in the All-Japan Sexy Commando Tournament. His mastery of this martial art, which prioritizes distraction techniques over brute force, gives him deep insight into the club's activities. Operating as Susan, he covertly guides and supports the club members, leveraging his expertise while maintaining his disguised identity and official position.