Sandra wrapped my throbbing horse shaft in her wet and warm tendril as another teased over the heavy balls that hung under them. What I wasn't ready for was the third that slipped underneath and thrust upwards, piercing wetly into my new entrance and wriggling around in eager exploration.
Cindy hissed in her own pleasure. "Don't stop that, for anything... yes..." It was easy to forget at times she shared my body, but I was too busy being blown away, quite literally, by Sandra's exploring tongues. She wasn't happy just tasting the throbbing flesh and soft spurts of prefluids, however, Keeping me held firm while pressing ever deeper, she turned away, extending her tongue as she went to keep me in her grasp the entire time.
Her tail raised high, she waggled her hips at me with plain intent. "I was your herd-sister first, and I want to be your favorite, the alpha queen just under you."
Her words and posture made me somehow harder, almost painfully erect and dribbling to the ground as something reacted to her. I wanted her. I wanted her as my alpha female. I couldn't help but think of her that way and I grabbed her hips, rubbing over her flanks softly a moment. Cindy sniffed loudly at the air. "Oh! She's deep in heat. No wonder she's so hot to trot."
Sandra perked an ear back at us. "I am? No wonder... Do it, fill me." She rocked her body a little as her tongues squeezed at me. The one lodged in my new cunt pressed fully in, wriggling around with a pleasure I never knew before. "Make me your special mare."
I couldn't say no to her, and she seemed to somehow know this as she withdrew the tongue that held my shaft. I moved up behind her and directed the tool, rubbing its blunt end slowly over her swollen lips. I could feel the heat radiating from them, and the moisture that seeped from her. She smelled powerfully. It was a stink, some part of me said, but it was outvoted by the rest that knew it was the smell of a mare in season that wanted no other stallion but me.
I pressed against her, sinking that tool into the velvety grip of her body, parting her tight tunnel and forcing it to conform to my considerable girth. Her tongues squeezed and flexed as she adjusted, grunting with pleasure and pain. The buzzing inside me grew in intensity my vision became partially obscured with a snout pushing out with the soft pops and cracks of adjusting bones. I was spared much of the pain, dulled in the pleasure of the moment.
Sandra's flank suddenly became warmer and she cried out in ecstatic howl. She had gained a cutie mark, the first I'd seen besides Luna, or the other princesses she'd shown me. I was a little distracted to take in the details, besides to see that a pattern had appeared. I was too busy mounting her even as pain ran hot through my ribs. I wanted to rut her. I had to, but whatever was changing was making it really hard to focus on it.
Sandra drove herself back, forcing my shaft deeper into the wet furnace of her body even as I heard a loud snap. With a burst of blood and viscera, new limbs broke free of me even as I gained in mass quickly. I fell forward onto the new legs, then standing over Sandra instead of kneeling behind her as the legs gained their own pink fur and rapidly bulked with muscles. I was a centaur, though at that moment, I was Sandra's centaur, and I began to ride her as she deserved, pistoning my horse dick deep into her as she howled and shuddered with building pleasure.
I dimly noticed the earth ponies that had been farming had gathered around to watch our wild rutting. Some of them even cheered and clopped their hooves on the ground as we went at it, encouraging us onwards. I didn't have the thought to pay much attention to them, as I only cared about Sandra at that moment. Her tongue squeezed and pulled at my balls, bidding them to empty, and they obeyed her. I could feel every pulse run down my shaft in a bulge before blasting out into her in waves of liquid heat and some undefined energy, eager to spark a fire within her. I could hear Cindy and my own's moans of satisfaction, though a small part noticed my voice sounded a little more feminine, as subtle as it was with my increased size.
My shaft twitched powerfully, filling Sandra's hungry womb as she ground herself back against me. She withdrew her tongues, though not without a parting lick over my puffy vulva, making me jump a little in place and grind that shaft against her from a new angle. As the cum began to backwash out and splatter on the floor, our audience became all the more interested, licking over their lips and murmuring among themselves.
"Enough! Back to work!" Crystal walked in, clopping her hooves together as she ambled along on her hind-legs. "Give them some privacy, even if they aren't asking for any." The ponies shrank before her mild fury and scattered back out into the fields, except one brave stallion that advanced on us with his own shaft twitching under him.
"Um, sir, ma'am? May I?" He was looking right at me and rocking a bit, making his shaft slap up against his furry belly.
Crystal advanced on him with a frown and he shrank back before retreating with a little whimper to the fields. Crystal turned to look at us, locked together, and shook her head slowly. "Well... good morning then." She fell back to all fours. "Is this... your final form then?" Her eyes wandered down to Sandra. "And are you alright? He looks a bit... oversized, to put it politely."
Sandra wriggled herself lightly. "I've never felt better than now."
Cindy let out a satisfied sigh. "We're all fine. And look, William is a pony now."
Crystal nodded at me. "I see that, but he still has hands?" She moved up and nuzzled one of those hands, fur-covered as they were. "You'll make the other ponies jealous, but you were already doing that mounting Sandra like that. She wouldn't let any other pony come close to her, and she raised her tail for you the moment you two were reunited."
I ran the hand over Crystal's ears and mane. She was right, she felt both furry and soft, and yet hard and smooth like a stone. "Sorry for, uh, what are the rules about this kind of thing these days?"
Crystal sat on her haunches. "Well this is my herd here." She made a wide gesture. "These ponies do as I command, and I try to run a civil ship, which you're setting a bad example at. It's hard, seeing as the urge to get wet and messy is still there and strong in many of my ponies, so they kiss and fuck when I'm not staring at them. The kissing I don't mind, but we're going to have a big problem when the mares start swelling up all at once."
The idea of that somehow made my flagging shaft twitch with renewed vigor, and I pulled back from Sandra carefully lest we end up rutting all over again. Cindy grinned at Crystal. "Well, sorry, but we just got Sandra on her way to family life."
Crystal sighed softly. "On one hand, we need to replace all the ponies being killed, on the other, unless ponies grow up fast, it'll just slow us down in the short term with half our population out of comission for a while."
Sandra tilted her head. "Hey, what happened to--" She paused as I slipped out of her, fluids gushing free to the ground as she shuddered. When she stopped leaking she sighed and resumed. "What happened to kids? You know, normal kids that got infected?"
Crystal shook her head. "We have a few of them here, if you want to meet them? They're adorable, but... they're also a bit lost. Most of them didn't have smooth transitions. Just... ugh... imagine a parent driven wild by the gift and what they might do..." She frowned sharply. "I try not to think about that. There's one herd that's almost all foals. A damn elementary school converted en-masse by a 'duchess', as Cindy puts it."