From Renta!:

Although things started out with Atsushi stumbling in on Mizuki in a compromising situation... they've finally become a couple. Mizuki's over the moon to be with Atsushi, one of the coolest and most popular guys on campus. However, due to the trauma of being tossed aside by his ex-coach and previous lover, Mizuki finds himself struggling with a lack of self-confidence that may lead to trouble ahead... This is a pure love story about an ex-player and a swimmer who's never had a real relationship. Includes previously unpublished content.