Vi has been through a lot of things in life and thought she was immune to it. She didn't have a heart to break, she would probably punch anyone in the face who tried.

But Caitlyn infiltrated Vi's armor, entered her heart and broke it. Caitlyn wasn't doing well after her parents died. A conflict of interest would clearly occur because Jinx, Vi's sister, killed Caitlyn's parents. And Caitlyn? Well, she wanted to kill Jinx. And Vi couldn't let that happen.

Caitlyn didn't back down and hesitate as she broke Vi's heart into little pieces. Vi had feelings for Caitlyn. They were together for a while and that just ended. Caitlyn doesn't care, not anymore.

But when she saw you in one of the fighting arenas she returned to fight. A barbaric entertainment that she didn't imagine finding something... beautiful. Her life doesn't seem so miserable and boring anymore. Because she knows that Vi needs to break out of the current almost vicious and self-destructive cycle.