The two combatants walked up to either side of the arena.
"In this corner, one of the four reigning princesses of Equestria, recently confirmed to have not been born an alicorn (no seriously, it's canon now), ruler of the moon and the night sky, Princess Luna!" Luna flew down regally into the arena.
"And in this corner, hailing from a planet I'm not even going to attempt to pronounce, with more fire power and inexplicable random master of powers than any non-mary sue should be allowed to possess, Starfire!" Starfire floated into the arena excitedly.
"Alright ladies, just a refresher on the new rules: the name of the game is making your opponent cum, preferably hard, by any means necessary, that hasn't changed. Weapons may be used, same goes for special abilities. Light combat is also allowed in order to make the opponent submit, and battling is allowed, if it must come down to it, though if your opponent tags out, you let them up. The winner advances to the next round, the loser is disqualified, and the loser spends two nights as the winner's sex slave."
Both girls nodded, Luna giving a regal bow, and Starfire politely returning the gesture as best she could with her body being bipedal and non-equine. This would be a battle between two equals.
"If the combatants are set," There was a pause, during which Luna's horn lit up brightly with her magic and Starfire's hands and eyes began to glow with her own power, "Begin!"
Luna and Starfire both took off flying at the same moment, rushing towards the center of the arena. Starfire began shooting energy bolts at Luna, and Luna returned fire with her magic. One of Luna's magic bolts blasted off Starfire's top, exposing her sizable orange chest. Seconds later, the two collided in the center.
"And Starfire has lost her top! It seems the two are caught in a grapple!"
Being an alicorn, Luna had all the strength of an earth pony and then some, and could counter Starfire's strength fairly well. Even then, if it was just a matter of strength, Starfire would have been winning out immediately. But Luna's magic was a factor as well, and was holding Starfire back. Luna pushed forward, pinning Starfire beneath her, and using her magic to remove the rest of her clothing.
"And Starfire is completely naked!"
Starfire shot a blast of energy from her eyes, but Luna deflected it with a shield spell. She then moved down Starfire's body, plunging her tongue into Starfire's pussy and probing it deep. Starfire moaned loudly, and continued to try to escape, but it was no use. Being unable to even move, held entirely in place, caused Starfire to feel every moment of the pleasure.
Starfire wondered for a moment how a princess had gotten so good with her tongue, and decided she'd have plenty of time to ask, considering where she would be for the next couple days. Starfire cried out loudly, swearing in her native language as she came hard.
"And Starfire has reached climax! Luna is the victor!"
Luna released her magical grip on Starfire. Starfire saw Luna's mouth covered in her juices, and leaned forward to kiss her, tasting herself on Luna's lips. Luna smiled, knowing that Starfire would be quite a loyal pet.
"Looks like Alicorns remain difficult to break. Next up is Arelie vs May! Will the runner take down the coordinator? Or will this race be no contest for May? Find out in the next round of Yuri Tournament!"