After graduating from dungeon-school, girl-dungeon-fairy Ciel was supposed to summon a boss-monster and make a dungeon. However, the dungeon-monster she ended up summoning was a slime.

Summoning a slime as a boss-monster was the lowest possible result, but as Ciel grieved over this, the slime suddenly spoke up in a human language. This is the full-fledged dungeon management success story of Tard, the lowly slime who can't even use magic and Ciel, the dungeon-fairy who had already given up on happiness!

Well, I say that, but the slime's subordinate is scouted with the help of a death-threat, the entrance of the dungeon becomes occupied by thieves, there is no way to know when they will be betrayed by their friends and other than dealing with the dungeon-management, they also have to put up with the troublesome people that arrive in the village.