"Return to that summer with you..." Ryusei returns to the small island of his younger years, where time flows by gently, to spend a fairy-tale summer vacation with his childhood friend who was spirited away.

Five years ago, Aoba Ryusei's childhood friend, Shinomiya Ginka, disappeared without a trace on the night of the summer festival. The superstitious islanders believed this to be an act of God, saying that she was "spirited away."

Now in high school, Ryusei decides to visit the island over summer break. He needs to know: Did Ginka ever come back? Could she be living a normal high school life?

Sadly, his faint hopes are crushed when he learns that Ginka was never seen again after that night. He dejectedly prepares to depart, but then he meets a young girl who looks exactly like his missing childhood friend― Ginka.

"Welcome back, Ryusei."

The girl doesn't know her own name. All she knows is that she loves Ryusei.

Where has she been? Why hasn't she aged? Finally reunited with his long lost friend, Ryusei vows to have the best summer vacation ever on the tranquil little island of his childhood.