The Kitahara family decides to return to their hometown during a long vacation. While looking forward to spending time with her son on a small trip, the familiar scenery of her childhood home deeply stirs Natsumi’s emotions. Greeted by her younger sister Reiko, whose warmth and smile remain unchanged, the long journey’s fatigue quickly fades away. Reiko, too, feels a strange tightness in her chest upon seeing Natsumi again after so long. Without much formal greeting, the sisters head indoors, laughing and playing like young girls. Their deep bond begins to take an unexpected turn. The shocking second act of an incestuous mother-daughter swap quietly begins.