Jeong Gu-won, a 200-year-old demon, loses his powers and relies on an ordinary human. Despite his role as a bodyguard and a sham marriage, he harbors genuine concern for this human. Often serious and observant, he also reveals a playful side as a joker and prankster. Revered for his extraordinary appearance by many girls, they're unaware he's a demon captivating their minds. His encounter with a human disrupts his perfect demon life, awakening emotions of love and care previously foreign to him.