The narrative centers on Masashi, who has recently returned to his hometown for work, and his old friend, Katsutoshi Ijichi. Despite having different lives, the two share a long-standing, deviant interest in "partner swapping." During a casual conversation, Katsutoshi suggests reviving their old hobby. Masashi is initially skeptical, uninterested in swapping wives as he feels they are "past their prime." However, the conversation takes a dark turn when Masashi realizes they both have something else in common: they each have an only daughter. The two men come to a mutual, disturbing agreement to "offer up" their own daughters as the subjects of their next swap. Driven by a mix of thrill and moral depravity, they decide to treat their children as partners for their exchange, prioritizing their own twisted desires over their roles as fathers.