Im Yoona is the spoiled daughter of a college dean.  Because her father is in charge of the whole campus, she does whatever she wants with no consequences whatsoever.  She personally enjoys torturing her fellow classmates and professors with useless and harsh pranks.  She shares a condominium with Yuri, Jessica, Sooyoung, and Seohyun.  Taeyeon, Sunny, Tiffany, and Hyoyeon live next door.  These nine girls are the only girls that know her inside out, and she built a tall barrier between her and others so she knows who her true friends are.  She is considered to be quite difficult, but she's one of the sweetest girls you will meet.  Yoona is very caring of her friends and family and goes out of her way to protect them.  She has been in love with Jiyong since their first year of high school, but he moves away to fulfill his dream of becoming an entertainer.  She bullied Seunghyun in the beginning of college and becomes his friend soon after.  What does she do when she starts to have feelings for Seunghyun?  Will her devotion for Jiyong stay or will she have no patience and turn to Seunghyun?

As the years go by, she becomes more mature and drops her bad girl attitude.  What caused her to have a sudden change of attitude?  She suddenly moved away in the middle of college to Jeju Island to avoid everyone in Seoul.  What if she is forced to come back?  How will everyone react to her sudden return?

Kwon Jiyong is Yoona's best friend of over a decade.  He is very ambitious and has big goals in life.  He moved to Los Angeles in hopes of breaking through as a singer and successfully does so.  Jiyong is known as G Dragon in the music industry and creates a big commotion in the country.  He goes back to Korea on hiatus after scandals with numerous women and is surprised to find Yoona close to someone else.  Jealousy fills him and he begins to finally develop feelings for Yoona.  Is it too late to win her back or will she run back to him with open arms?

After some time, his feelings for Yoona remain, but what if she shuns him away?  He is surprised to see Yoona as a new woman throughout the years.  Her attitude is more responsible and she is more mature.  What will he have to do to win her back?

Seunghyun moved to Korea suddenly and emerged in Yoona's campus out of the blue.  He becomes the main topic of everyone's gossip to why he moved and why he was so quiet.  Seunghyun turns out to be a man of layers and a painful past.  He befriends Yoona even if she bullied him.  Yoona is a woman that intrigues him because she is the only woman that isn't afraid of his scary looks.  She was the only one daring enough to bully him and the only one to try to get to know him.  He starts to fall for Yoona slowly.  He starts a rivalry with Jiyong after he discovers that he was her first love.  His past friendship with Jiyong in the United States is tested when the both of them fall for the same woman.

Taeyeon, Jessica, Sunny, Tiffany, Hyoyeon, Yuri, Sooyoung, and Seohyun are the women that Yoona are the closest to.  They are Yoona's support and backbone during her hardships.  They offer her advice that really helps her and get through that problem.  Yoona is especially close to Jessica, Yuri, Sooyoung, and Seohyun because they were like her sisters since kindergarten.  Tiffany, Taeyeon, Hyoyeon, and Sunny are like her older sisters.  They keep her tamed when she is angry.

Daesung, Taeyang, and Seungri are Seunghyun's younger brothers.  They have different personalities and are a bundle load of trouble for Seunghyun.  Seunghyun cares about them deeply and loves them to death.  They follow in their hyung's footsteps by pursuing Yoona's friends because of their natural beauty and great personality.

Jaejoong and Hyun Joong are Seunghyun's best friends.  They are in support of Yoona and Seunghyun and often tease Seunghyun when Yoona is not present that they are perfect for each other.  They are also friends with Jiyong, but favor Seunghyun.  Jaejoong is in a relationship with Taeyeon while Hyun Joong is chasing after Tiffany.