According to legend, there is a secret tunnel in Japan that can grant any wish — the Urashima Tunnel. When Kaoru stumbles upon it by chance, his deepest desire is to bring his deceased sister back to life. Kaoru ventures into the tunnel — and meets his new classmate Anzu, an outsider with hidden wishes of her own. Together, they decide to uncover the secret of the tunnel. But the fulfillment of their wishes comes at a high price...