Kaoru Touno"s family is falling apart. After a sibling dies and his parents split, he finds no calm at home. Following a heated argument with his father, Kaoru leaves the house and discovers a strange tunnel that pulls him in. Confused by what he sees inside, he rushes toward the exit, picking up a bird that looks exactly like his lost pet on the way out.
When he emerges outside, Kaoru realizes that although only minutes passed inside, a whole week has gone by. The odd experience brings to mind the legend of the "Urashima Tunnel"—a passage that grants wishes in exchange for one"s life. With his bird resurrected, Kaoru wonders if another visit could fix his broken world.
However, when he returns to the tunnel"s entrance, Kaoru notices that Anzu Hanashiro, a new transfer student in his class, has followed him. She knows about the rumor and asks for his help with an experiment—she too has a wish that only the tunnel can grant.
