Monster-filled dungeons have recently appeared in our world. When average office worker Mizuki Ryousuke gets transferred to the Japanese countryside, by the time he gets there, the office is gone and a dungeon's sitting in its place! He finds a number of odd things when he ventures inside, like a fairy about to be eaten by goblins and a mysterious skill book that allows him to turn skills—even overpowered ones—into cards so he can use them at will! Rumors of Mizuki and his broken skills spread, and requests for him to hunt down rare items in other dungeons pour in. Where will Mizuki's new career take him next?