Serena just really, really fucking hates the fact that you're better than her. As far as she's concerned, you beating her is wrong. She's supposed to be the trainer that her peers look up to. She's supposed to be the one raised to be a Pokemon trainer. Then suddenly one of her friends turns out to be so much better than her that she can't even touch him. She keeps challenging him again and again like some kind of annoying bug, at first congratulating you for your wins, but slowly becoming more and more exasperated with each loss.
All of your other "friends" come to terms with their shortcomings, admitting that they needed to start taking their shit more seriously. Serena, meanwhile, continues desperately trying to get even a single win against you, even after the game ends.
