Is It Wrong to Try to Pick Up Girls in a Dungeon?: Is It Wrong to Expect a Hot Spring in a Dungeon?

After the crisis on the eighteenth floor of the Dungeon, Bell Cranel, Hestia and their companions set off back toward the surface. Exhausted by their ordeal, they hope to rest briefly before returning to Orario, when they unexpectedly stumble upon a hidden area that appears on no ordinary map of the Dungeon. Beyond the rock walls lies a hot spring, surrounded by greenery and practically untouched by other adventurers. Mikoto is especially delighted, since she has long dreamed of a chance to unwind after so many battles, and the rest of the party also decides to make the most of the opportunity to relax.

Hestia quickly sees the spring as a chance to spend time alone with Bell, but her plans run into the other girls, who also want to be near him, and a simple soak turns into yet another rivalry. Hermes notices the situation and decides to have some fun at everyone else's expense, much to the irritation of Asfi and the girls, while Bell ends up at the center of the commotion without meaning to. The peace does not last: the water suddenly changes color, a strange phenomenon begins dissolving the bathers' clothing, and monsters appear. The hot spring is no ordinary natural feature, and it hides an evil secret.