Do-Hee's life takes a dramatic turn when she encounters Jeong Gu-won, a centuries-old demon who thrives on striking deals with humans. Their fates intertwine unexpectedly when they are mystically bound together, creating a dynamic relationship that begins with tension and suspicion but slowly evolves into mutual reliance and eventually love. Do-hee challenges Gu-won’s cynical view of humanity with her quiet strength and unwavering determination, while he forces her to confront her fears of vulnerability and trust. Their bond not only brings thrilling romance but also allows her to rediscover her softer, more open-hearted side.