This film stops trying to solve Kaede and just lets her exist as a person carrying weight she never asked to hold. The mystery isn't the point; watching Sakuta finally understand what his sister actually needs from him is. Everything the series built toward, the fractured family, the unsaid things, the small moments that matter more than supernatural explanations, crystallizes in a single conversation that rewrites what you thought you were watching all along.

As March arrives and Mai Sakurajima's high school graduation day comes, Sakuta Azusagawa waits for his girlfriend at Shichirigahama beach. There he meets an elementary school girl who looks just like Mai did in her child actress days, but she vanishes once the real Mai shows up. Back home, Sakuta finds an unfamiliar scar on his body and suspects another case of Puberty Syndrome. Then his father calls: their mother, long hospitalized after struggling to cope with what happened to Kaede, now wants to see her daughter. Sakuta, openly nervous, agrees to a meeting that has been a long time coming, as more strange scars appear. The film is a supernatural, psychological romance drama based on the ninth light novel volume.