Celestia's bicentennial demonstration of Equine dominance over the dragons by way of massive futa horsecock.

“So what - “ Twilight paused in her question as the sound of Princess Celestia’s grunts briefly overwhelmed her hearing, then resumed as soon as she could hear her own voice again. “What exactly is the significance of this event again?”

“It’s - unf - an Equestria tradition,” Celestia grunted. She paused and wiped her forehead. The dragon - just an adolescent, it seemed, its scales a bright burnished red - moved straight up in the air, speared, as he was, on Celestia’s massive member. The bulge in his stomach from just the head (which was, apparently, all he could take. Even that, Twilight noted, was more than impressive) was an obscene, enormous sort of bulge that was itself almost the size of the rest of his body.

“See, Twilight,” Celestia said, “ruling Equestria isn’t easy.” She leaned back on her haunches, letting her massive, mostly uncovered cock bob and weave in the air. The dragon on top of it just mostly gurgled as Celestia’s golden magic surrounded him, gently moving him up and down the length of her flare like a (comparatively) tiny little cocksock.

“You’ve got - mmff - nations on all sides trying to top you. You’d think that ruling the Sun and Moon would help keep your control over the region? Not at all.” Celestia bit her lip, a pair of yellow auras springing up around her massive, haystack-sized balls and massaging them gently. “Oh, that’s much better.

“But in any case, that just means that I had to get more creative,” Celestia said. She wiped her forehead, though whether it was sweat or precum, it was too hard to tell. Twilight just scribbled down some notes. “You have to - nggh - really show the dragons who’s boss. Get in their faces, as they say. And, as dragons are such naturally sexual creatures - “

Celestia’s face momentarily screwed up as her hips thrust into the air. Her giant balls swelled, pulled together - and then her cock was spewing dozens and dozens of gallons of thick, hot Princess seed inside of the red dragon on her tip. He squirmed and thrashed, his little legs smacking against her shaft, but a twenty-foot-long, six-foot-wide cock didn’t budge easily. As it was, it only served to intensify Celestia’s orgasm, the Princess biting down on her lip and squeezing her eyes shut as an aquarium’s value in cum came flooding into the dragon’s belly, swelling it outward and outward like a used condom until finally he plopped to the ground, belly first, and steadily leaking from his abused asshole.

“See?” Celestia said lightly. Twilight applauded, her notebook momentarily forgotten. “Just like that.”

“Do see that he’s able to digest all of that,” Celestia said to a passing dragon, whose own spread asshole was clearly visible despite his much larger size. “He was such a good cumsock, and I’d hate for it to go to waste.”

“Yes, Princess,” the dragon said, bowing. He leaned down and picked up the smaller adolescent’s in his claws, then dragged him along the field like a water balloon.

“Ah,” Celestia said. She leaned forward on her balls and sighed happily. “It’s so nice to see a species that knows its place. So much better than all of the nags at the Gala. Oh, Irontooth!”

An enormous black dragon - fifty feet tall at the shoulder, at least - thudded to a stop before the Equestrian pair. “Is it my turn, Princess?”

“Always, my dear Irontooth.” Celestia grinned sultrily at him. “Now pucker up.”

Irontooth knelt down on the grass, lifting his tail high and presenting his ass to the world. Celestia grinned down at Twilight.

“Take note, Twilight,” she said. “Because sometimes, you’ll need to use other magic during this ceremony. For example…”

A golden aura surrounded her, and Celestia moaned as she began to grow. She’d always been tall as a pony, reaching about an even six feet, but now she was reaching seven - no, fifteen - no, forty feet! Twilight watched in awe as her mentor finally petered out to an incredible seventy feet in height, her twenty-foot-long package suddenly seeming much more manageable on a pony of that gigantic size.

“Size shifting,” Celestia said, her towering form nearly blotting out the sun as she took a hold of Irontooth’s tail with one hoof and lined up her throbbing, leaking shaft with the other, “is an often essential tool when dealing with naturally larger lifeforms. Magic is, of course, an important part of balancing the scales, and an alicorn’s magic doubly so.”

Twilight paused in her notes to watch in academic interest as Celestia eased her cock head into Irontooth’s backdoor, then slammed herself the rest of the way in. The dragon let out an earthshaking roar, but the rumbling of Celestia’s balls was an earthquake all of its own.

“Now - mmff - remember,” Celestia breathed, bottoming out inside of Irontooth, “that this is a bicentennial - unf - ceremony, and as such - “ she grunted again “ - must be done to leave a - guh - lasting impression.” Irontooth bellowed again as a massive, ten-foot bulge pushed out from his stomach, then bellowed again as Celestia’s gigantic balls smacked into his tender, spread rump.

“O-o-oh!” Celestia flung her head back, her eyes rolling up as she came. Her enormous balls actually retracted toward her body, her cock swelling up at the base before the orgasm broke free. Hundreds of thousands of gallons of cum spewed into Irontooth’s rear, filling him up and more as Celestia rode her much smaller partner for another thirty seconds.

Finally, with Irontooth’s belly nice and round with cum, Celestia’s orgasm stopped. She panted happily as he slid off, groaning with pleasure.

“That’s how you do it,” Celestia said. She smiled tiredly down at Twilight. “Any questions?”

Twilight shook her head. “Good,” Celestia said, patting her mountainous cock. “When we get back, we’ll have to have you practice on Spike.

“It’ll be good for the two of you, I think.”