Kim Seojun is one of the famous bad boys of their academy. A rebel who only knows how to bully and cause trouble. He was a good boy before the girl who he truly loved passes away. She died from cancer at a young age. He felt that his world tore apart when she left. He was too dedicated to her that he became the opposite of who he was. Furthermore, he became afraid to love again, thinking that he'll only be left behind again. Not only that, but he became the bad boy who doesn't care about anyone's feelings anymore. Until a transferee named Yoon Mara came into his life. She's two years younger than him. He once tried to bully her but ended up being beaten by her. An issue began leaking about what happened. He was embarrassed by this and thought of revenge. So, he made her his servant. Yup, a miserable servant. She has no choice but to follow everything, he's going to tell her. They hate each other so much. But as time passes, their feelings for each other are slowly turning upside down. Will it be the way to change him back to who he was? Will she be the reason for him to love again? How if he finds out that she's the sister of the woman who he loved? Will he ignore his past to live in the present, or ignore the present to continue living in the past?