Minako is the mother of her biological son Yoichi and her stepson Takeshi. Yoichi is a spoiled child who has not yet been weaned and continues to drink Minako's breast milk. Having to watch this every day, Takeshi begins to masturbate to the fantasy of himself drinking breast milk. Unable to be satisfied with just that, he finally approaches Minako and drinks her breast milk... and they end up engaging in mother-son incest. Takeshi regrets this act, but Minako, sensing his feelings, accepts him again.