My sister's boyfriend is a walking red flag

Lee Dong - Min is one of the most successful students in the school, he is the class president, he is good in sports, he is the team captain in every sport, he is handsome (all the girls fall for him), he is good everything. He dates a beautiful girl, Hwang Da - Eun that admired him from primary school. She is the youngest sister of Hwang SuHo, he is in same class with Dong - Min and is his sworn enemy. SuHo is always second in everything, always Dong - Min is first. He would never imagine what would happen after a meeting of this two.