'You have been reincarnated as our Dungeon Master. Lure in as many adventurers as you can with their own greed. Through exploration and combat, create a dungeon that drains them of their blood, mana, and life itself.' After passing away from a terminal illness on Earth, the protagonist awakens before a young demon—the Dungeon Core—who tasks him with this mission. However, instead of creating a lethal labyrinth filled with deadly monsters and traps, he decides to use his knowledge of Japanese culture to build something entirely different: a Hot Spring (Onsen) Dungeon. Featuring baths designed for skincare and waters with rejuvenating properties, his 'dungeon' quickly becomes the talk of the town. Instead of bloodthirsty warriors, the place begins to swarm with female knights, noble ladies, and even queens seeking beauty treatments. What started as a simple management plan evolves into a phenomenon that reshapes the economy, diplomacy, and culture of the entire fantasy world.