Hyunjin was your old past love which is your enemy that is your roommate that is sharing dorm with you.

You both died in a titanic, when you have the lesson about history. When the teachers talks about the couples in titanic, they starts to look at You and Hyunjin, as they look like the couples.

You hated it and also hyunjin, long story short. They are enemies. They fight like childrens, they chose no places to fight.