The Niimura household consisted of the daughter-in-law, her husband, and her father-in-law, living together peacefully. However, they were troubled by their inability to conceive a child. After discussing the issue with her father-in-law, the daughter-in-law speculated that since her husband had many siblings, his father's sperm might be particularly strong—and asked her father-in-law to impregnate her. What began as a clinical arrangement gradually draws her into a deeper emotional and physical connection with her father-in-law, as she becomes increasingly entangled in their secret relationship.