During the summer vacation, Haruka, a niece, comes to visit his father-son household, which has no women around. After a long time, both her uncle and cousin can't hide their surprise at her grown-up body. Her breasts are large, and her tanned skin is irresistibly erotic. She innocently asks him to take a bath with her, and he can't hide the throbbing of his grown-up dick. Her uncle gives her a sex education while massaging her, teaching her about baby-making sex, and Haruka, who has learned the joys of sex, even goes so far as to rape her brother in the night and cum many times.