Natsu e no tunnel, sayonara no deguchi

According to legend, there is a secret tunnel in the mountains of Japan where any wish can be granted - the Urashima Tunnel. When Kaoru hears about it, he immediately sets out to find it. Ever since his little sister Karen died in an accident, he has wanted nothing more than to see her again. Kaoru finds the tunnel - and meets his new classmate Anzu there, who is also an outsider with hidden desires. They decide to get to the bottom of the tunnel's secret together. But the fulfillment of their wishes comes at a high price ...