You've beaten the Sinnoh Champion Cynthia. Before the fight, she had promised you a special reward in addition to the champion slot, and now she's guiding you into the next room for your bonus prize.

"Come on champion! I have a surprise for you."

You let her guide you into the next room, where she locks the door behind you. She pulls off some clothing, revealing a cow tail? And cow ears? Horns? A pair of udders? Cynthia pulls off her fake nose, revealing a real one with a nosering. She's a real damn cowgirl!

"I'm your prize, champion. Come on, claim your milk. I'm yours."