I was sure I had a big, dumb grin on my face, but I didn't care. I was still enjoying the afterglow of seeing Rainbow Dash swallow a mouthful my cum – or, at least, what was mostly my cum. Even though it had come from Twilight's using my bottom half, even though she'd twice pumped it into the purple tail-end I was using now, I still thought of that dick as mine. I had an attachment to it, even when I wasn't actually attached.

“So, Rainbow, you want to know what it feels like when Shining's on top of me?” Twilight asked.

Rainbow nodded, a confident smirk on her face. She gave a significant look toward my dick, watching it swing limply between my sister's legs.

Twilight matched her with a smirk of her own.

I'd only ever had Twilight's mare parts, never anypony else's. This would be interesting. Would Rainbow's hind end feel different than Twilight's? Then again, would the two of them even give me any attention at all? They'd have what they needed all on their own. Sitting here alone on the bed for any longer sure wasn't very appealing. I resolved to at least clop myself with Rainbow's pussy. If they ignored me, I could still at least have a little fun... plus, they'd be fun to watch.

Her horn glowing fiercely, Twilight concentrated hard – I knew it because she was sticking her tongue out, something she rarely did anymore.

This time, there were two flashes of her spell. I looked down, but instead of a pair of pale blue teats, I found my own familiar sheath and nuts. I looked up at the two of them.

They were a perfect matched set; one blue and purple, the other purple and blue. Twilight had simply switched the back halves of the two mares around. That suited me just fine. I was glad to have my familiar maleness back... and was quickly starting to anticipate what I'd be doing with it, which had a noticeable effect on its size and stiffness.

“Like what you see, brother?”

I nodded.

Rainbow glanced back and forth between me and Twilight. “Wha...? I don't get it. I thought you were going to show me what it's like to get boned by your brother.”

“Who said I was going to do it? To really get the big brother experience, you need the big brother himself. Isn't that right—” she looked at me, pointedly letting her eyes drop down to my package “—big brother?”

I nodded, grinning.

Rainbow shrugged and turned her tail to me, flipping it high over her back. “Well then, come on and get some, big brother!”

I didn't have to be told twice. I bounded off of the bed and practically ran up behind her. She flicked Twilight's purple tail high, brushing it up against my nose. The raunchy smell of sex wafting from it nearly overwhelmed my senses. She fluffed her blue wings out and winked Twilight's pussy at me, showing me tantalizing glimpses of my sister's pink inner walls, still liberally coated with different white and clear gooey liquids.

I mounted her, ready to shove myself in eagerly, but something took hold of my dick – something warm, soft and wet. Glancing down and back, I saw Twilight reaching her head under my belly. Her mouth pulled my tool up to meet perfectly up with Rainbow's borrowed pussy, pressing it against the steamy entrance. Taking a moment to admire it, I reveled in the novel feeling of my sister's mouth and pussy touching my dick at the same time. Then I pressed forward.

Twilight's already well-used lips opened easily, letting my shaft glide into it smoothly with no resistance at all.

Rainbow took it like a champ. “Oh Fuh... Fff... Unh! Oh my gosh, Twi! He's so deep inside!”

I pushed in farther, sliding all the way into her until her lips twitched and pulsed around the very base of my dick.

“Your pussy takes him in so easily!” Panting, Rainbow looked over her shoulder at Twilight. “And so deep! I can feel him, Twi. It feels like he's splitting me down the middle with that thing. Damn I love wrapping your pussy around it!”

Twilight grinned at her and moved closer, slipping a forehoof between Rainbow's back legs to tickle her teats, massage her thighs, and even reach all the way through, past where the two of us joined sloppily together to gently fondle my balls. “He's great, isn't he?”

I slid out of that oh-so-familiar pussy and slammed back in again before Rainbow could respond. All she was able to give was a startled gasp and then a deep moan as she melted in pleasure, her front legs collapsing underneath her.

Rainbow only lasted through two thrusts before she finished. As I slid back into her borrowed pussy's comforting embrace, she clamped down hard on it and squirted all over my back legs, spraying them with an intoxicating mixture of juices. I pressed into as hard as I could, feeling her convulse around me, pulling me in deeper and deeper, trying to use Twilight's pussy to milk me dry.

“Now that's interesting,” Twilight mused. “So it must be that Rainbow's speed to orgasm is dependent upon her mental faculties, not her physical attributes.”

Rainbow glared at her. “Could you stop studying for one minute— Ah!”

I'd started moving again, grinning down at her as I did, knowing what it would do to her.

“You're such a— Unf! ...an egghead!” With a little, high-pitched scream, Rainbow came again, her whole body jittering and shaking with the force of the erotic pleasure coursing through her.

...And I was just getting started! As I began to find my rhythm, I pounded into her jellified insides ruthlessly, giving her my full measure as a stallion. I didn't slow at all when she came again and again, soaking both of us with Twilight's juices. The little mare, once so feisty and now a shuddering wreck, bit down on one of her front hooves to quiet her cries and rode out orgasm after orgasm as I plowed her face into the soft carpet.

Finally, I began to get close to my own limits. I could feel the tingling, the static buzz of sensation curling from my dick through my spine and around my whole body, the insatiable need to slide farther and farther into her inviting hole.

“Come on, brother, you wouldn't ignore your little sis, would you?”

Twilight must have heard my grunting pants and known what it meant. I pulled out of Rainbow, leaving her collapsed and sweating on the floor, far beyond being able to complain about my absence... and I turned to face my sister, my beautiful adorkable sister.

She presented her ass to me... or, rather, she presented Rainbow's ass to me. Where Twilight's was soft and inviting, Rainbow's was all smooth and firm edges, powerful muscles squeezed into a tiny, perfectly shaped package. And in the middle of the deep, supple cleft of her ass cheeks, her prim and petite little snatch dribbled out a trail of clean, clear fluids that slowly flowed down her inner thighs.

I wasted no time in mounting her, and Twilight didn't allow for any fumbling. Her magic took hold of me and pulled me into just the right place right away. I let the pressure of my dick build against that tight little pussy, squishing it against the solid muscles around it, before it finally stretched enough to admit me and I plunged my tip inside with a satisfying plop. I could feel the ring of her entrance pressing around my shaft, feel it sink lower and lower around it, stretching wider and wider as it went. But beyond that constricting little ring, she was softer and more pliable than any mare I'd ever had, conforming to every contour of my dick without the slightest resistance.

Twilight moaned, then yelped as I bottomed out in Rainbow's pussy. “Aah! Not so deep!”

I pulled back slightly, wondering how Rainbow herself had taken it from Twilight if it was so uncomfortable. Maybe that little mare was just too tough to allow a little pressure on her cervix to stop her fun...

“Ah, yes. That's better.” Twilight wiggled Rainbow's rump around my dick, moving it around inside her. “Wow, she sure is sensitive. I don't know if I'll be able to last very long when you— Aah!”

I resumed my previous pace without warning, easily sliding in and out despite the constriction of Rainbow's tightly stretched entrance. Still, I pressed into her carefully, not wanting to cause Twiley any discomfort. Of course, I hadn't lost much progress after leaving Rainbow. Once again, I felt my dick beginning to swell even bigger.

Twilight hissed her breaths and opened Rainbow's legs as wide as she could, trying to accommodate the massive shaft pushing in and out of her, relieving some of the pressure.

That wasn't what I wanted.

I took her blue hind legs in my magic and shoved them together. Oh yes, that was better. Of course, I could always... I grinned, and moved her legs even farther, pushing one forward and pulling one back until they crossed.

She moaned and whined, and she tried to move side to side, but I held her there, still pushing into her in a quick rhythm. I could feel her pussy bulging from the pressure, pressing out around the base of my dick to rub against my medial ring instead of letting it rub against her firm ass cheeks like it had before. I grunted, panting heavily. I wouldn’t last much longer.

By then, Rainbow had come around, though she still rested on the floor in a puddle of Twilight's love-juices. She stared at us, grinning, for a moment, but then her grin faded and her eyes shot open wide. “Hey!” She shouted. “You'd better not be about to—”

It was too late. I grunted, pushing a thick bulge of hot cum through her constricting entrance and spilling it deep inside her. It filled her, coating her insides with virile seed, filling her to the brim. I'd never gotten off like that before. It just kept coming and coming, wave after wave of it flowing into her snatch, squeezing against her tight passage and flooding the softness beyond. Every twitch pulsed the bottom side of my dick against my sister's borrowed – and extremely sensitive – clit.

Twilight finally gave out. She cried out and came hard, using Rainbow's well-trained muscles to squeeze down on me and tease out every last drop.

Except, of course, her pussy was already overfilled with stallion meat and swirling cum. When she squeezed down, it all had only one place to go. Even as stretched as it was, the tight ring of Rainbow's entrance couldn't hold back the flood anymore. It sprayed out in a ring around all sides of my dick, squirting out with incredible force. Clear and white alike, it struck my thighs and spewed from them, scattering droplets over a huge area.

I glanced at Rainbow. She was staring at us, eyes wide and mouth moving soundlessly. A couple white drops had landed on her forehead, and another one slid down the tip of her nose. It would drip into her mouth soon if she didn't notice it first.

Pulling out of Twilight's borrowed pussy wasn't hard, especially when a new pulse of her inner muscles all but shoved my softening dick out. Another flood of the sticky white mess followed as we separated, splattering noisily on the already-soaked carpet.

Rainbow finally found her voice. “Twilight! You, you... You can't do that to me!”

Twilight just grinned back at her friend with an incredibly satisfied look that somehow mixed smugness with completely fulfilled sexual desire. “You know, I've read about it, but I never really believed it could be true... They say that a mare can feel it when she's impregnated, when a stallion's sperm finds her eggs. I believe it now – I can feel it, Rainbow. I can feel that new life inside me!”

“No! No! No!” Rainbow blanched, her face a mask of absolute horror. “It can't... you can't... Aaugh!”

Twilight giggled. “Oh Rainbow, you are such an easy mark.”

“Huh?”

“You should have seen your face just now! Did you really think I wouldn't add a simple contraception spell to the mix when I did all these body swap spells? I'm not a stupid mare, and I'm not about to risk creating the incestuously marred babies that would come from me and my brother. Besides, I have no idea what all this body swapping might do to the delicate hormonal balance of an early developing zygote.”

“Oh, right...” Rainbow rose up from the floor, still breathing heavily. “Magic.”

I laughed a little at that. Twiley did always have a somewhat twisted sense of humor.

But then there was a slight tapping on the window.

We all looked, and when I saw her, I could feel the blood drain from my face... it felt like the blood drained from my whole body. The room was suddenly too cold, too small, and far too constricting, closing in around me. Princess Cadance looked in through the window, one eyebrow raised haughtily. I'd been caught in the act... by the most powerful mare in the Crystal Empire: my wife.

Author's Note

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