Kazuki Tsukigase is a high school boy who carries a certain secret. In search of a place where no one knows him, he enrolls at Sakijima High School on a remote island. On Sakijima, there is a place known as the "Cove of Spiriting Away." One early summer day, Kazuki finds a girl lying unconscious in the cove. The girl—Nanao, 16 years old—later regains consciousness in the hospital, but her identity remains unknown. What is the meaning behind the word "1974" that she murmured?