Gyu Min Ae, loves her brother to bits. CNBlue, a not so typical group of badboys. One accident led to Min Ae's brother into a state of a life or death situation and has not woken up in a long while. 
The sadness Min Ae had for her brother, has now transformed into anger. And seeking revenge was the one and only thing that occupies on her mind. Min Ae decided that the best way of revenge was by breaking it through the core and joins them without letting them know she was Dong Min's sister.

"Sorry oppa. I'm sorry. I'm confused...I can't do this anymore," 

Yonghwa, the leader of the group and JongHyun has gotten Min Ae confused with her plans and with her own feelings.