Kazuki Tsukigase is a high school boy carrying a secret he wishes to hide from everyone. In his search for a place where no one knows his past, he transfers to Sakijima High School, located on a remote and isolated island. This new environment, far from his previous life, is meant to be a fresh start.

On this island, there is a mysterious location known as the Cove of Spiriting Away, a place rumored to be connected to mysterious disappearances. During an early summer day, Kazuki explores this cove and makes a startling discovery: a girl lying unconscious. He rushes her to a clinic, and when she eventually wakes up, she reveals that her name is Nanao and she is sixteen years old. Aside from these basic facts, her identity remains a complete unknown. She has no memory of who she is or how she ended up on the island. The only clue she can offer is a single, cryptic word she murmurs: 1974.

As Kazuki finds himself drawn into the mystery surrounding Nanao, he begins to unravel the meaning behind that number and its connection to her appearance. The narrative unfolds as a touching and emotional boy-meets-girl story, weaving together elements of romance and mystery. Set against the backdrop of the isolated island community, the story follows Kazuki and Nanao as they navigate her lost memories and the strange circumstances of their meeting, building a relationship while trying to uncover the truth behind the enigma of the year 1974.