Ken's father-in-law asks when he will finally provide a grandchild, turning a family hot-spring trip into pressure to impregnate his wife. Ken follows instructions and abstains for a month, only for his wife to refuse sex on the trip. Frustrated, he wanders the inn and accidentally sees his adult mother-in-law bathing. One forbidden encounter leads him to forget himself, creampie her repeatedly, and face the possibility that he has made his wife's mother pregnant.