After a fight with her husband, Keisuke's aunt Mio comes to live with him for a while. Keisuke admires Mio and has feelings for her as a member of the opposite sex. While he is living there, his heart pounding at the sight of her huge breasts, he finds Mio's panties left in the bathroom. He can't help but masturbate, but Mio witnesses it. Mio, who has a free-spirited personality, comes over to Keisuke while he is taking a bath late at night and gently strokes his penis before inserting it into her vagina.