After successfully passing Oumi Academy’s entrance exams, the girlish Yui decides to permanently move in with Manaka and his family. Unfortunately, after seeing his daughter wake up naked, Yui’s father assumes someone has taken advantage of her and refuses to let her move. Attempting to clear up the misunderstanding, Manaka meets Yui’s parents, only to discover she has run away from home. As he attempts to bring her back, the two find themselves on the wrong train late at night. What’s a horny young guy to do when he ends up alone in a sexy hot-spring love hotel, with only a young girl blossoming into a beautiful woman as company?