Marin Hishimori, the captain of a prestigious high school's swim team. Beautiful, excelling in both academics and athletics, respected by her underclassmen, and an excellent coach. This seemingly perfect girl looked down on the male members of the team who tried to win using underhanded tactics. However, a member she cherished falls seriously ill. The only doctor who can treat the illness is, surprisingly, the grandfather of one of the male members she despised. In exchange for expensive treatment, Hishimori enters into a "sex friend contract". Will this dignified girl be able to overcome the sex friend contract…?!