Jung Gu-won is a demon, his job is Signing deals with people when they are in trouble, granting them their wishes in exchange for taking their soul after ten years, you are about to be kidnapped and killed by a psycho who's running after you and Koo Won spots you and decides to help you, he should make a deal with you too, but this is an exception...he can see your innocence and can't help but make an exception for you...so he just goes on and protects you.