Now I'm a Demon Lord! Happily Ever After with Monster Girls in My Dungeon

Yuki finds himself reincarnated as a demon lord in another world, and he's been put in charge of a dungeon to boot! Once Yuki accepts that his fate hinges on the dungeon's survival in a world where powerful monsters roam free and danger lurks at every corner, he begins gathering allies and bolstering his defenses. Within a few days, he takes on a legendary dragon, an adorable pet slime, and a vampire girl, but despite all his precautions, life as a demon lord in a dungeon constantly under threat...is surprisingly mellow?

Yuki's been reborn in another world as a demon lord—and his new life is going swimmingly! He continues strengthening his dungeon with his makeshift family of monster girls until, one day, a heroine arrives on their doorstep to take down the demon lord. Or, at least, that's what she says before breaking into tears because the traps are too scary! Curious and unable to resist lending a helping hand, Yuki heads out to welcome the hapless heroine.