The Killer (Jugeodo Doeneun Ai)

Ui-gang is a hit man who has decided to retire. He has a nice house and all the money he needs, but one day his girlfriend takes a trip to Jeju Island and leaves him with a request. Her companion on the trip has a 17-year old daughter Yoon-ji who will be left alone during their three week vacation. Ui-gang reluctantly agrees to look after Yoon-ji and make sure she doesn't get into trouble.