On the day of Mai Sakurajima's high school graduation, Sakuta Azusagawa encounters an elementary schooler on the Shichirigahama shore who looks exactly like Mai as a child, another manifestation of Adolescence Syndrome. At the same time, Sakuta's hospitalized mother reaches out for a family reunion, forcing him to confront the years he spent raising his sister Kaede alone and the resentment he buried. This third film in the series closes the high-school arc of Sakuta's story.