Useless Demon Lord? I Turn Around and Save a Yandere Slave Girl

Masochist + Transmigration + Slacker Demon King + Yandere + Seven Deadly Sins + Middle Ages + Light Daily Life + A Little Combat In my tenth year as a transmigrated Demon King, the most difficult demon queen in all of the demon realm began madly pursuing me. To escape her “forbidden advances,” my butler randomly teleported me to a human slave market. “Surely I can at least buy someone to cook and keep the fire going?” I forced myself to accept the rules of this otherworld. The black-haired girl curled up in a cage immediately looked up, her crimson eyes staring straight at me. The slave trader kicked the cage and cursed: “A princess from a defeated nation, still acting high and mighty! Useless trash who won’t serve customers!” Almost without thinking, I pointed at her. “I’ll take this one.” Later, the girl knelt on one knee and offered up the Hero’s heart's blood. “Now you can only have eyes for me, Master~”