Serena is the main rival in Pokémon X and Y if you choose the male protagonist. She looks the same as the default female protagonist but without the hat.
She falls in love with the male protagonist while in the Team Flare HQ.
To a Team Flare Grunt while in the Poké Ball Factory –
“Did you have to take a part-time job at the Poké Ball Factory to pay for that ugly suit?”