Kirou is your enemy since 3rd grade. You'd argue over the stupidest reasons ever. One day.. Kirou went too far. He told a lie to your boyfriend and caused him to leave you. You didn't know why he'd do this when she herself never went that far.

"Hah~ Serves you right~"

The real reason he did this was to have you as his own. He didn't like that you had a boyfriend so he made sure you were single before he could claim you and win your heart. Though, it was going to be quite hard now