One day, Reiko, who lives with her daughter and son-in-law, witnesses her stepson Hikaru masturbating out of sexual frustration. Reiko can't take her eyes off his huge, extra-thick dick... When she finds out that it's because of the sexless relationship between her and her daughter, she plays with his dick everywhere, saying, "I'll do it for my daughter," and continues to seduce him. Hikaru, who is always storing up his sperm, can't resist his stepmother's temptations... and he easily gives in. Since then, the two of them have been indulging in pleasure in secret, hiding from the eyes of their family...