Underwater lovey-dovey sex with a mermaid girlfriend! Kou and his childhood friend and girlfriend, Marina, come to the school pool on a day off. Marina, who is of fish-man descent, teaches Kou how to swim, but she forcefully buries his face in her voluptuous breasts and gives him an underwater footjob. The pleasure makes Kou's penis erect, and he then ejaculates with an underwater blowjob. Unable to calm down, the two move to the changing room, where Kou enjoys the soft skin and pressure of her breasts through breastfeeding play and a boob job, ejaculating again. Eventually, Marina asks for penetration, so Kou inserts his erect penis into her vagina and starts pounding her violently from behind...