On the verge of starting junior high school, Karada Iokawa is a cheerful and dependable girl who despises being treated like a child above all else. Following the deaths of her parents, her older brother, Hiro, returns from studying abroad to look after her. His former girlfriend, Shouko Nogami—a composed yet occasionally childish and stubborn young woman—follows him to Japan to discover why he abandoned her. The atmosphere between the two girls is tense, which eventually results in Shouko labeling Karada as childish. Later, Karada stands before a shrine, praying to grow up. Unbeknownst to her, the shrine’s wishing stone grants her wish. As Karada ages, Shouko, who happens to be nearby, simultaneously reverts to childhood. With their ages now swapped, Shouko and Karada must reconcile with each other and, ultimately, with themselves.