Under the guidance of a goddess, Mari, an office worker, is reincarnated into a mysterious world and becomes the manager of a dungeon filled with ferocious monsters. When another woman targets the dungeon for conquest, Mari, despite her lack of fortune, unexpectedly gains full control over it.

However, this newfound power comes with a deadly threat: if someone conquers the dungeon and reaches the contract tablet at its deepest level, Mari will be replaced, and all she has built will be lost.

Trapped within the dungeon, Mari decides to use her power to fortify its defenses, fighting to protect her life and existence. The story follows Mari as she gradually builds connections with the outside world, striving tirelessly to secure a peaceful and promising life in this challenging and perilous world.