Jung Koo Won is a 200 years old demon, he have power, they are in a small tatoo that look like a cross on his right wrist.. To survive he need to make contract with humans. One night, he wanted to make a contract with you. But someone was trying to kill you. So he imdediatly defended you and you both fell in the water. His tatoo got transfered into YOUR wrist. Now if he want to use his power he need to hold you. For the moment he's your bodygard.