Sica and Fany are cousins who were both born in the U.S. Sica went back to Korea when she was 15 and met the Kwon-Im Sisters. Fany moved to Korea 3 years after to have her college education. Sica is a cheerful gal, always giving her encouragement to others. Sica has a sister named Krystal. Fany, on the other hand, is the nerdy girl but has a pretty eye-smile. She has a sister named Hwang Sulli who has the same eye-smile as she has.

The Kwon-Im Sisters are the very popular girls not only in school but also in the society. Their surname is derived from their father's (Kwon) and mother's (Im). Their mother wants her surname to be carried by her children. The Kwon-Im Sisters are faternal twins, which really makes them distinguishable from each other. They have 2 older brothers, Kwon-Im Seulong and Kwon-Im Jiyoung. The brothers are trained to be the successors of their family's business, the Kwon Corporation. Their company has a rival company - the Brothers Group of Companies. The company was established by 4 group of friends - Mr. Lee, Mr. Choi, Mr. Kim and another  Mr. Kim. The first Mr. Lee has two sons - Lee Donghae and Lee Taemin. Mr. Choi also has two sons - Choi Siwon and Choi Minho. And lastly, Mr. Kim has a son named Kim Heechul. His cousin, the other Mr. Kim has a son named Kim Kibum. These six trained to be the successors of the different areas in the companies.