Main leads:-

Lee Jung Suk: Son of multibillioner, also known as prankster with a friendly nature and kind-hearted natured but also brat. 

Kim Hyun Joong: Also son of multibillioner, but with cold heart and emotionless person with a calm personatiliy. Helpful to his friend and is a choosy person.

Oh Yeon Joo:  A simple girl with calm nature shy type, is a tranferred student is a mature type girl.

Doo Hu Mi: A simple girl with bubbly nature who is talkative  with childish character loves HELLO KITTY! Is also transferred student.

Read to know how this person's meet and fall in LOVE  !!