Zubu Nure no Ane Kasumi "Watashi no Mizugi ni Sonna Kitanai Mono, Shimikomasenaide!"

Ryusuke belongs to the male swimming club. But one day, the club is forced to close down because of an accident. He asks Kasumi, his older step sister, not to close down, but she ignores it. After all, he joins the female swimming club to do chores. "I'll get even with you someday...." One day, he accidentally sees Kasumi masturbating in the club room....