Byun Baekhyun and Choi Hee-Soo are childhood buddies .She's a normal high-school girl .A beauty ,smart and independant  and comes from somewhat rich family .Nothing special .Highschool is never easy ,but it's not unbearable .While for Baekhyun ,he's currently a trainee at one of the biggest company in entertainment industry ,SM Ent .Adopted by Hee-Soo's parents after the accident that killed his parents ,he always see her parents as his own ,and see Hee-Soo as his sister .While for Hee-Soo ,he was never a brother ,and never just a friend .

"How can I love you when you're my sister ?"- Baekhyun 

"If you can't leave me ,then make me happy"- Hee-Soo