Park Jiyeon as Park Jiyeon

A daughter of rich family until her parents were killed by a mystery person when she was 18. Then she got into an accidents when she rushed to the hospital and lost all of her memory. After all that, Jiyeon lives in a small house on the rooftop. Jiyeon is a cheerful girl yet sometimes she is a bit stubborn and she is caring too.

Kai as Kai

A young assistants who work for the mystery person that kill Jiyeon's family. He gets paid a huge amount of money to kill Jiyeon. Kai has to pretend that he is just a normal person who rent a room in Jiyeon's small house. He will spends at Jiyeon's house for 5 months to approach her first. Must marry to Krystal after kill Jiyeon

Krystal Jung as Krystal Jung

A daughter of the mystery persons who try to kill Jiyeon's family. Krystal likes Kai very much when she first she him when he cames to her parents office. So Krystal tells her parents that she wants to marry him and her parents agree to it. Her parents paid a huge amount of money to Kai to kill Jiyeon and marry Krystal and he agrees to it.