Lucifer, a human being who was assimilated by a mysterious demon girl, came to the human world and accidentally picked up a girl who was similar to his sister when he was a human being. He suddenly took her to live with her on a whim. But the so-called fate is unpredictable... He killed his only sister. He slaughtered the demons and demon kings of the demon world on the verge of collapse. The gears of fate slowly turned. Will the ending be peaceful in this life, or will sin finally become the king...