You're actually in a complicated situation; being adopted by the Oh family who has an extremely good looking son named Oh Sehun and crushing on Lu Han the school playboy which is actually Sehun's arch nemesis. What would you do? 

(You) Oh Iseul. Smart, playful, a bit blunt and down to earth. Iseul's parents died in a car accident when she was five. And now, she's a part of the Oh family. Currently crushing on Lu Han the school playboy. 

Oh Sehun. The only son of Oh Corporation as well as Iseul's step older brother. A bit cold, and can be over protective towards Iseul. Sehun is secretly crushing on her since the first time they met. But he knows it doesn't feels right to date his own sister. He has a grudge against Lu Han for a reason.

Lu Han. A good looking and popular chinese boy at school. He is mischievous and tends to be easily irritated. He is the son of the richest man in Beijing who owns the Lu Corporation.