Masuda Keima just wants to sleep. Too bad for him, he's been pulled from comfy sheets into a fantasy dungeon that he's charged to protect. Failing to do so will cost him his life. His only guide on what to do is the personification of the Dungeon Core, Rokuko. But she's a moron who can't even figure out how to get rid of a group of bandits. If Keima ever wants to get some sweet dreams again, he'll have to do all the planning himself!