Kim Shinmi and Oh Sehun are childhood friends. They were close and relied to each other like they were siblings. However, due to Shinmi's parent's business, they had to move to China at the age of 9. Sehun clearly was devastated by the news. He changed drastically ever since. Bullying students that are weaker than him became his daily routine. 

7 years later, Shinmi moved back to Seoul. Sadly, she had forgotten about Sehun and he was determined to make her remember. 

Oh Sehun

Kim Shinmi