Both feature a male lead with split personality (Kill Me Heal Me has several personalities while Gap Dong only has two) and an unpredictable plot based around mystery. However Kill Me Heal Me is for the most part more light-hearted and comedic than the rather heavy storyline of Gap Dong.
The same psychopath killer type of story that relates to both female and male lead. Both female and male leads develop feeling in process of finding out the truth. Although in Gap Dong there are no supernatural power that plays in the drama
