Koel was running from a mistake he knew he'd never be able to fix, a mistake that ate at his very soul. He resigned himself to a life of loneliness and fear, always aware that he had screwed up big time.
But when he discovers a strange knife and finds himself stuck in an ancient contract with a demon, he doesn't know whether to be happy or horrified. On the one hand, his time alone has come to an end. On the other, the demon is violent and cruel, hateful toward all humankind--who had bound him to the knife and forced the demon to serve whoever owned the knife for millennia.
The demon chooses to use Koel as much as he can while being subjected to a life of servitude due to the curse. He sees his new master as a completely amateur and naive human, someone who can easily be manipulated but also someone whose morals enrage him. But when Koel offers to find a way to free the demon from his curse, he finds himself caught up in Koel's complex life--something he'd never expected to happen.