Lazy Dungeon Master (Manga) Volume. 1
In this fantasy isekai tale, one slacker gets a rude awakening when he becomes the guardian of a dungeon!Masuda Keima just wants to sleep. Too bad for him, he's been pulled from sweet dreams and comfy sheets into a fantasy dungeon in another world! Not only is he charged with protecting it, but failure to do so will cost him his life. His only guide is the personification of the Dungeon Core, Rokuko--but she's a moron who can't even figure out how to drive away a group of bandits. If Keima ever wants to get some quality shut-eye again, he'll have to take over running this dungeon himself!