Natsu e no Tunnel, Sayonara no Deguchi

Kaoru Touno has never escaped the grief of losing his younger sister when he hears about the Urashima Tunnel, a place rumored to grant a person's deepest wish in exchange for years of life. Finding it proves that time inside moves differently and that the rumor may be real. Transfer student Anzu Hanashiro discovers his secret and, carrying a desperate wish of her own, agrees to investigate the tunnel with him rather than rush inside blindly. Their careful experiments draw them closer over the summer, until a path meant to recover what was lost becomes a choice between the past they cannot release and the future beginning to form between them.