When Koichi's mother-in-law asks when she will finally see a grandchild, he is shaken to learn that the family hot-spring trip is partly meant to make him conceive with his wife. He abstains for a month as instructed, only for his wife to refuse sex when the trip begins. Restless and frustrated, he wanders through the inn and accidentally sees his mother-in-law bathing. Desire takes over, leading him to repeatedly creampie her during the trip and leave her pregnant with a secret he can never confess to his wife.