Choi Ae-Ra used to be the only girl who could handle Han Seo Jun. He used to find her annoying but when she turned 16, she definitely got his attention. Ae-Ra hides a lot of stuff from Han Seo Jun due to the mental abuse she receives from her father and eventually loses him. 

After tragic events, Choi Ae-Ra finally returns to school to try and get things back to how they were only to find Han Seo Jun has possibly moved on and has absolutely no interest in hearing what she has to say.