When I Was Reincarnated into the World of an Ultra-Difficult Game, I Ended Up As the Sole Subordinate of the Ridiculously Strong yet Incompetent Demon Lord, Tasked with Creating a Dungeon

I was deemed a failure by the goddess and ended up reincarnated into the world of a game known for its insanely high difficulty, as the final boss’s Demon Lord. My skill is Dungeon Master, and my race is Demon—clearly, I’m on the enemy’s side, not the hero’s… Lost and confused, I encounter an overwhelmingly powerful being… Wait, you’re the Demon Lord? You defeated the heroes but lost your subordinates and dungeons and now have no motivation…? I seem to have some useful skills, so could I serve you as a tool?