Natsu e no Tunnel, Sayonara no Deguchi

There is a strange rumor surrounding the Urashima Tunnel: it grants the wish of those who enter at the cost of their lifespan. Kaoru Touno did not think much of this silly urban legend until he stumbled across a dark tunnel one night. Initially dismissing the idea of going in, Kaoru is enticed by the possibility of bringing back his sister, Karen. Karen had died in an accident five years prior as a result of Kaoru's carelessness. As he enters the tunnel, what Kaoru discovers within is not quite