The Black-Hearted Devil's Sanatorium

I am Azaz, the cursed demon king, who once made the entire continent fearful. Now? I'm broke. My magic power was exhausted, creditors came to visit me, and my territory was deserted—I was about to be forced to take over the house by the Demon Bank. With no other choice, I made a decision that went against my ancestors: to turn the Demon King's Castle into a sanatorium. Use curses to cure diseases, use threats to collect money, use succubus to collect debts at the front desk, and let the headless horseman act as a security guard to control the scene.