Even though he wanted a small room, what he ended up creating was a vast and powerful dungeon. Chrono, an ordinary demon, creates a dungeon at the Demon King's Castle academy. It's a custom for demons to create a dungeon in the Demon King's castle when they turn twenty, live there, study hard, and become independent. Chrono thought he'd make a small dungeon, but what he ended up with was a gigantic structure with hundreds of floors. It was an unbelievably high level, surpassing even the dungeons made by legendary demon lords. "I just wanted a small dungeon...!" Chrono, who wanted a simple and easy life, quickly became the center of attention and rose through the ranks of the demons, eventually becoming known as a hero.