One night, Kaori, wearing only her underwear, comes to Sota's room seeking help. Sota is shocked, but it turns out the club members were holding a strip mahjong tournament. With Kaori facing certain defeat, she makes a last-ditch effort to recruit Sota as her substitute player. The tournament's grand prize was... the right to do whatever they wanted with Sota?! Reluctant but needing to protect himself, Sota joins the game. Meanwhile, Kaori seems to have her own thoughts on the matter...