Ae-cha / you : A 22 year old surgical assistant at Cecil Street Medical Clinic in New York. It was your dying father's wish for you to help others in some way and to have a bright future. You are a very introverted person who can't make friends easily. You are also very clumsy at times but always try your best to do good. You have never dated in your life due to your awkward personality. You have a pet taby cat named Prince who lives in your small apartment. Also, you are a very caring person and have a hard time letting go of something / someone dear to you.

 Lee Kiseop : A 24 year old surgeon who developed psychopathic behavior at a young age. His current location is in New York, working in Cecil Street Medical Clinic. He commits regular murders around the U.S (mostly young women) and sometimes patients. He is the most wanted criminal in the U.S currently. Puts on a charming act to get what he wants. He has never experienced real love before (romantic relationship kind of love) and has a lack of empathy for his victims.

Jee Seung : Ae-cha's rival. She is very outgoing and gets any guy she wants. She acts kind to everyone except Ae-cha. Works as a nurse in Cecil Street Medical Clinic and is highly loved by everyone working there except Ae-cha. She is stuck up, egoistic and puts on a fake image to please everyone. 

 Kevin Woo : A badass, 23 year old detective. He has been on the psychopath case for 2 years with the FBI and believes he is close to catching the criminal. He has a shy personality but opens up as you get to know him.

 Bak Kyung : Ae-cha's bestfriend. Works as a nanny and is 23 years old. Supports Ae-cha alot and has grown up with her. Very outgoing personality, and is very adventurous. Is not affraid of pushing her limits most of the time.