After years of working for a black company that flaunted labor laws with excessive overtime and a lack of proper compensation, the protagonist finally quits his job. While contemplating his future, he stumbles upon a job advertisement for a dungeon tester. Intrigued, he applies and discovers a hidden fantasy world within modern society. The novel follows his journey as he works for the Demon Lord's army, testing dungeons designed to be impenetrable by heroes. This is a story of a man who finds a new life and purpose in an unexpected place, filled with adventure, challenges, and the satisfaction of overcoming adversity.