While waiting for Mai Sakurajima at the shoreline on her senior graduation day, Sakuta Azusagawa stumbles upon a younger rendition of Mai from her early acting career. Yet when the real Mai finally arrives, the child‑era version vanishes, leaving him bewildered. Upon returning home, Sakuta notices an unfamiliar mark on his skin, confirming his suspicion—he is facing another instance of the mysterious Puberty Syndrome.
Soon after, Sakuta and his sister Kaede receive a phone call from their father. He informs them that their mother, recently released from the hospital, wishes to see her daughter one more time. During a visit with Kaede at his mother"s side, Sakuta encounters odd phenomena and must find a way to resolve the Puberty Syndrome irregularities.
