Kim(Hero) Jaejoong is a killer but prefer to be called bodyguard, since he was young his father made him practise to be the guy he is today,he didn't want his son to be a victim of anyone.In the age of 6 he lost his parents and was left alone,so he closed his heart to anyone that tried to help him or get close to him after the night he saw his parents death by his own eyes he became a cruel monster thirsty for revenge and blood, after 13 years staying in a house with two  really close friends of his parents that found him and took him in their home to protect him and make him practise so that he can protect himself, his parents best friends The Family Jung found him and gave him a home,a place to call home and asked him only one thing :Now in the age of 24  he had the job to protect the leader of the most dangerous mafia team Jung Yunho,but without him noticing it.