Chic, serious Son Ga-in works as a GM in daesung international . Being the 'only' child of Son family, she was made to give up her dream to be a singer and to prepare herself to inherit her father's company. Her friends from Nega Networks and her childhood friend, Im Seulong were there for her. (She didn't like her job but was serious about it since she knew it's a commitment she had to keep as the only child of the Sons, she had to do her best since she is responsible for the company)

Unbeknownst to her, her father had an extramarital affair and had illegitimate children, Jo Kwon and Jo Mi Hye (Miryo). Only Miryo knew her mother was the third party. Miryo was one of Ga-in friends from Nega Networks. Even though she knew all along Ga-in was her stepsister, she bore no hate for her.

Jo Kwon, not knowing about the secret, fell in love with Ga-in and she, likewise, fell for Jo Kwon. (cheesy:b)

You know what to expect. 

Main Characters:

Son Ga-in
-Daughter of CEO of daesung international , GM of daesung international
-wanted to be a singer, supposed to be a member of BEG
-Likes Jokwon

Jo Kwon
-Leader of 2am
-Illegitimate son of Mr Son, stepbrother of Son Ga-in
-Likes Ga-in

Im Seulong
-Part of 2am
-Son Ga-in's best friend ever since childhood
-Likes Ga-in

Jo Mi-hye (Miryo)
-Illegitimate daughter of Mr Son, stepsister of Son Ga-in
-Older sister of Jo Kwon
-Likes Seulong
-Solo rapper of Nega Networks

Park Jin Young
- CEO of JYP entertainment, 2am's agency
- Likes Ga-in

Park Hye-rin (Raina)
-Likes Jokwon
-Jokwon's childhood friend
-Daughter of Park Jin Young

Mr Son
-Father of Son Ga-in, Jo Kwon, Miryo
- CEO of daesung international

Mrs Son
-Mother of Son Ga-in

Aunt Jo
- Mother of Jo Kwon, Miryo

Minor characters:

Kim Eana and Lee Min soo
-Lyricist and Producer of Nega Networks
-Best friends of Son Ga-in

Kim Hyo Jin (JeA)
-Solo singer of Nega Networks

Park Hyo Jin (Narsha)
- Changmin's girlfriend
- Actress in Nega Network

Lee Changmin
-Narsha's boyfriend
-Part of 2am

Jung Jinwoon
-Part of 2am