Rumor had it that the Urashima Tunnel defied the laws of space and time. Walk through it and your heart's desire awaits on the other side, though at the cost of your own precious years. Kaoru Tono heard this rumor and found himself standing before a tunnel that bore an eerie resemblance to the one in the tale. Karen, his sister who passed away five years prior, weighed heavily on his mind. Unexpectedly, Anzu Hanashiro, a new transfer student, accompanied him and suggested they explore the enigmatic tunnel together. But what does Anzu desire from Kaoru in return for her assistance, and how much would he have left to sacrifice when the tunnel has had its way with him?