Kazuki Tsukigase, harboring a certain secret, enrolls in Saikijima High School on a remote island in search of an environment where no one knows him. On Saikijima, there is a place known as the “Cove of Spiriting Away.” At the start of summer, Kazuki discovers a girl collapsed there. When she regains consciousness in the hospital, she gives her name as Nanao, age 16—and she has no known identity. What could be the meaning behind the mysterious word “1974” that Nanao whispered?