Shining groaned as the pulse of magical energy surged through his body. It was always such a strange feeling... like his skin was being stretched too tightly, bursting outwards as his body and muscles surged and rippled under its taut outer layer. The sag of his balls was even stranger, his two orbs bulging and sinking with their sudden added heft, causing a strange tension in his guts as the sensitive bits pressed against one another before his sack finally expanded for their new, hefty size.

And his cock.

It came in waves, like it usually would when he and Cadence played with the potion. Every two or three seconds… first a wave would make him thicken - his already fat black base getting vascular and girthy… then the next would throb out his length - stretching outwards a half-inch at a time… then one would reach his cockhead - blossoming his knobby unflared head wider, flatter…

Usually, he wasn’t inside Cadence when this happened.

And definitely he wasn’t inside his little sister.

“O-oh… oh… oh f-fUCK!” Twilight moaned and threw her head back as one his girth throbs stretched her with an audible squelch.

“T-twi…” Shining gasped, barely finding the breath to be able to speak in between the intense sensations of his body bulking into the physique of a large earth-stallion. He could feel Twily’s… his little sister’s… pussy celnching all around him, her tight walls not able to handle his growing size.

“S-sh… Shiny... i-it’s... “ Twilight panted, her eyes wide with sensation as she looked up at him. Another wave slid through him, and he felt his cock slip deeper into the smaller mare’s depths, pressing against some pink-flesh obstruction deep within her small body. “...mnngh! ...t-too… m-much…” She groaned tucking her chin to her chest and shutting her eye. Shining could feel her whole body coiled around him, tightening up with tension. Small tremors shivered through her velvet, twisting tunnel.

With broad, muscular, shoulders and heavy, powerful muscles he felt the potion finishing the transformation of his body into what amounted to an earth-pony physique… But there was one last big, final wave coming. He tried his best to warn his sibling.

“Oh. F-fuck Twi!” A huge pulse rippled through his phallus. Everything straining at once, his fat base expanding to the size of a foreleg… his whole length four inches longer than before… his saucer-plate shaped head trembling with blood-pressure… and his donut-shaped medial ring sliding into the stretched pink inner princess pussy-lips of his little sister, bumping right past her engorged clit as it did so.

“OH Fuck! Sh-shiny…!” Twilight eyes shot open in panic, pupils shrunk to pinpricks. She was gasping and hiccuping as she squeaked with convulsive bounces. She was blinking and thrashing her head, trying to hold something back, in a desperate fight to maintain control.

A fight she was losing.

“Oh, b-buck… I’m… I’m…. Sh-shinnnneeeeeeeeeeeeeeeey!!!”

Shining felt his little sister clench her forelegs even tighter against him, drawing her body up against his with an arched spine, trying to press herself as hard as she could against his belly. Rolling contractions rippled up the length of his buried stallion-cock, milking waves of sucking clenches, each tighter than anything Shining could have ever imagined.

“Ah! Ah! Ah! AHHH!” Staccato yelps came with each of her convulsions.

He felt Twilight’s hips tilting and grinding up into him for the first time, sinking more of his massive, fat cock inside her with each orgasmic shudder. The sensation of his little sister’s hot, swollen, winking clitoris grinding against the top of his shaft as it slid in and out with Twily’s spasming muscles was surreal.

“F-F-FUUUUUUUUU…….!” Her shout rumbled through her ribcage, an animal cry of pleasure… He felt hot blasts of sticky wetness splattering all over his balls, his inner thighs, his stomach as she coated him in a splattering spatter of her sticky filly-ejaculation. Wet and sloppy slaps accompanied her shudders, as her hips drove her soaking pussy against his body.

All Shining could do was hold on, desperately clenching his jaw and trying not to get lost in the lust of the moment - the burning heat engulfing his cock, the wet slapping sounds, the moaning mewls of a mare.

This was his little sister cumming on his cock.

“….UUuuuuuuunnghhh……” Her scream finally petered out - as did her shaking, straining, humping orgasmic convulsions, slowing and finally stopping as she went limp in the bindings… leaving only a dripping mess of clear mare-nectar waterfalling to the ground underneath them in gossamer strands.
.
He felt her fore-legs go loose around his shoulders, Twilight resting in the tight embrace of the bindings with exhausted, gasping little breaths as she struggled to recover from her orgasm.

Shining watched her, her rosy cheeks wet with tears of exertion… her brow and mane tousled and sweaty… eyes closed gently as she savored her post-orgasmic cocktail of pleasure… her pacific, contented-smile…

‘Why is my sister so damn…. cute?’

He watched her, trying his best not to move… not to react to the odd quiver or clench of her hot snatch around his cock… trying not to breathe on her ecstatic face. Trying to give her a few minutes of what seemed like joy.

But her eyes fluttered open af last - dopey, drunken rolling pupils looked up at him with a silly grin… his sister was still high on the potent sexual neurochemical flush.

“Y-you OK, Twily?” Shining asked, trying to avoid the mirth creeping into his voice at the sight of his spaced-out sister.

This seemed to bring Twilight back to herself. She nodded groggily at first, blinking, again and again, to clear her eyes of the fog. Her head shaking slightly to get some blood flow back into her head.

“Mmm...hm…” All at once, her consciousness seemed to rush back to her. He could see the change spread across the features of her face from pure, unrestrained pleasure… to mortified embarrassment.

She blinked away tears, whether of embarrassment or exhaustion he wasn’t sure - but the last thing he wanted was for her to feel upset.

“Twilight it’s perfectly-”

“I don’t wanna talk about it!” She squeaked, puffing her cheeks out and looking away to the side.

“Ok, sure.” Shining turned his head politely to the other side as well, giving his sister what space he could - despite the fact that he was invading her personal space with at least twelve inches of his body.

A wet dripping patter made the silence less than sustainable.

“I can’t believe I… came on my brother’s… dick…” Twilight muttered to herself.

“Do you always… are you always so… splashy?” Shining asked, Cadence never soaked his balls this much.

Twilight turned to look at him, fiery fury in her eyes. She glared at him for a moment before finally responding. “...N-no.”

“Ah… well… sorry.” He sagged slightly. It was hard to focus on not putting his hoof in his mouth when every other moment a clench would remind him he was deep inside his sister’s cunt.

Twilight let out a sigh under him and shook her head. “D-don’t be… you didn’t… do anything wrong…”

“S-still…”

“And… it... “ She tucked her chin down, avoiding looking at him as she squeaked out, barely audible… “...you… felt good.”

“Ah.” Shining stared away from his sister, not wanting her to see his face in that moment.

“Y-yeah.”

Shining felt a set of squeezes pinching the base of his cock, in a rhythm that could only be deliberate. He quickly turned and locked eyes with her… she was looking back at him shyly, but with some coy curiosity mixed into her grin.

“Do I… feel good?” Twilight asked, a small squeeze hugging his cock as she did so.

“T-Twily!” Shining stammered.

“Wh-what?”

“You’re my little sister!”

“So?”

“So I can’t tell my little sister that her pussy feels amazing! That’s just… wrong.”

Twilight giggled slightly and blushed. “It feels… amazing?”

“...T-twi…”

“What? C’mon… w-we’re stuck like this anyways…” She stammered. “I’m still a mare y-you know… I could use a little confidence boost.”

Shining felt his heart melt a little bit. He’d always tried to convince the socially shut in Twilight that she was far more attractive than she thought she was… “T-twi…”

“W-we used to share everything with each other. No secrets right?” Twilight hurriedly added. As if that applied at all. “Remember?”

Another milking quiver as her purple cunt contracted around his throbbing black length. Shining found himself reciprocating humping forward with a jerk of his groin muscles, throbbing his cock inside her and jamming the edge of his head’s ridge against the fleshy ceiling of the deepest part of her vaginal wall.

“Mm!” Twilight squeaked with surprise. Sexy, pleasurable surprise. Damn why was she sounding so hot!?

“S-sorry…” He muttered.

“D-don’t be… your cock feels freakin’ amazing.”

“Twi!”

“What!? It does - I’m gonna have to go and replace all my little toys with the extra-extra large size ones.” She giggled. “I never realized I would like… big ones so much.” She looked up at him with a coy eyebrow. “Maybe I could use one of those clone-a-stallion packs on you?”

“Twilight!” He sputtered, thoughts of his little-sister masturbating herself on a silicon version of his cock filling his mind. “Stop!”

“Oh come on…. Maybe I’m just a bit giddy, but...” Twilight laughed aloud. “We’re stuck like this anyway… might as well have a good attitude about it… I won’t stop teasing you until you tell me.”

“Tell you what?”

“Tell me what…” Twilight bit her lip. He felt another squeezing clenching hug around his cock. “...you think of me…”

“...”

Another squeeze, this one hard enough to press her fat clit against him.

“Fuck it.” Shining breathed. “Your body is so damn sexy Twilight… you feel so bucking good.”

Twilight stopped giggling, a deeper blush replacing her rosy cheeks. Both siblings fell into silence. No squeezing or twitching.

A few moments later, Twilight spoke up.

“Shiney… I love you.”

Shining felt it like an apple-farmer’s kick to his heart. He didn’t even have to think about his reply, it had been as true now in this crazy situation as it ever had been.

“I love you too, Twi.”

“...So… w-what if… y-you…. Y’know…” Twilight mumbled.

Shining looked down at her and arched an eyebrow in confusion. “If I….”

“M-made… love… with me.”

“Uhm…” Shining couldn’t help but flex himself, scraping his little sister’s insides with his girth, reminding her of the positions they were in.

“Mmf! N-no… I mean… if you moved… and... “ She locked eyes with him and breathed out. “Finished in me.”

Shining felt a flood of hot blood throb through his brain. It was exciting enough to hear his wife ask to have him fill her with baby batter… but to have his sister ask him!

“T-twi!? W-we…”

“I mean… y-you’re not gonna go soft anytime soon.” She quickly explained.

“That’s for sure.” No chance of that happening while he was buried in mareflesh.

“S-so… maybe if you finished… you’d go soft… and then we could get out….” She looked up at him, rosey cheeks burning brightly, eyes full of desire and hope, sparkling with dewy love.

“Y-yeah…” It made no sense. None whatsoever. Even if he went soft - they would still be bound up with one another. There was no mistaking it - this was his sister asking him to fuck her. “A-are you sure you w-want me to...:?”

Twilight nodded. “A-and y-you want to… also, right?”

Shining looked down at her, filled with apprehension, tension, lust, desire… and love. Gods. Everything about this screamed taboo, screamed wrong… His mind played through the decades of time that he had grown up with Twilight. Always filled with love and friendship… but never - this. It was so wrong.

And yet.

Everything aside from his mind. His heart. His gut. His cock… OK, he tried to tune that last one down a little bit. Back to his heart: it was overflowing with love for his little sister. His Twily.

Twilight.

He couldn’t let her down.

“Y-yeah. B-but wh-what about… foals…”

Twilight bit her lip. “I… I don’t know. I’m not sure if I’m in estrus or not. But…

“But…”

“It… wouldn’t be the end of the world if I had your foal.”

“Mm… y-you’d be a great mom.”

“Y-you’re already a great dad.”

They stared at each other, drunk on one another’s love for a full minute, enjoying the sensation of their bodies and their hearts.

“Shiney…”

“Twily…”

“C-can y-you give me… a kiss?”

He was already leaning down even as she began to request it. He kept his eyes open, not wanting to miss a second of the sight as their lips contacted. He watched his little sister’s tension melt out of her features, clenched shut eyes relaxing… and felt a ripple through her pussy as she moaned into his lips, her soft breath tickling his nose.

It was lighting a fire in him.

He slid his tongue against her lips, slipping into her muzzle and widening her mouth as he turned their kiss into a deeper, Prench kiss. Her soft moan became a throaty growl as he probed the back of her throat. And then he began to thrust.

“MMmmmmf!” She groaned into his kiss as he started to slide massive, throbbing black stallionflesh into her slick pussy. His huge length was quickly running out of space - he was already buried deep, deep within his sister’s pussy… and she could only take a couple more inches before he was pressing against her cervix.

As soon as his flare pressed against her final barrier Twilight broke away from their kiss and tossed her head backward. “O-oh f-fuck!” The bulge in her body was at her belly button. A sudden burst of ripples flooded through her tight little cunt, rapid, disorganized spasms of milking clenches as she humped back into his slow thrust… sending winking squirts shooting against his thighs from her third orgasm of the afternoon - he felt her tail swish and lash against his lower legs, her whole plot quivering and tightening, her ponut and dock tensing and relaxing with the waves of orgasm.

He couldn’t take any more of this.

He stumbled forward, jamming Twilight against the wall of the zeppelin’s cabin, finding purchase to start thrusting with more intensity - letting him stuff more of himself into his little sister’s needy cunt.

“Oh… f-fuck…. Sh-shiney!”

He was pumping in and out now, his grinding hips sliding a few inches of his gargantuan earth-pony-like cock in and out of Twilight’s body. Pump after pump, his fat, black cockhead battering against his little sister’s womb.

“Y-yes…. Yes!”

His heavy black balls began to swing as his thrusting increased in speed and intensity, swinging and impacting with wet plaps against Twilight’s dock and soaked tailhole, drenched from a constant flow of hot, sticky marecum.

“MMMMnnnngh! Oh Clestiat!”

Twilight had tucked her head against his powerful chest, bringing her horn just into range of his mouth. Without even thinking, he let the purple horn into his mouth, nibbling at it the same way that Cadence loved when he did during their more passionate sessions.

It was like a bomb went off in his mouth.

“H-HOLY FUUUUUCKING F-FUCK!” Twilight screamed beneath him.

The sparkling gunpowder taste in his mouth was a brief distraction, before the rippling and terrifyingly powerful fourth orgasm of his little sister’s spasming body overwhelmed him. She was humping and gyrating against him with violence, her wings flapping wildly out to their sides in a desperate attempt to get a little bit more leverage to impale herself on her brother’s fat, throbbing stud-cock.

And the deeply ingrained biological instincts of stallion and broodmare were triggered in the siblings - hips slamming with more force, cock throbbing with more blood…. womb opening to be bred.

Shining felt the last few inches of his cock slid into his little sister’s cunt suddenly, as he fucked his fat cockhead deep into her womb.

Twilight immediately wrenched her head backward, pulling her horn out of his mouth in a cascade of purple fireworks as she continue to cum all over her brother’s magically fattened cock as he jackhammered her into the wall/

“OH BUCK! SHINING! SHINING! SHINING!” Twilight moans

*PLAP PLAP PLAP*

“BUCK! BUCK ME! YES! YES!”

*PLAP PLAP PLAP*

Their bodies were completely merged, a sweaty twisting mass of flesh and fur, the musky stink of their sweaty and engorged, dripping sexes surrounding them like a fog. Everything was pleasure and pain - an aching tension of burning muscles and potent hormones, driving him to pound harder… harder… harder!

*PLAP PLAP PLAP*

“Twiiiii-aaaaaahhHH!” He screamed out, biting his tongue and clenching his jaw… powerful muscles straining and bulging as he felt his cockhead expand to it’s a full, massive, throbbing pre-orgasmic flare, his heavy balls shot up to his groin and he felt the agonic throes of his orgasm as it began… a thick pulse traveling through his groin like a broken spring.

He was going to pop in Twily - there was no way to stop now. The little filly he’d given horsey-back rides to. That he’d cheered up when she was blue. That he’d pulled goofy pranks on.

He was going to paint her insides white.

Fill her with his fertile side.

He was going to cum in his little sister.

*PLAP PLAP PLAP*

“ShhineeeeEEeee….” Twilight groaned out, eyes rolling wildly, tongue hanging loosely from one as she succumbed to the wild final thrusts of his final and desperate passion.

His cock-slit exploded thick, boiling, fertile stallion-seed.

A loud crack and POOF of smoke filled the entire room.

…

Unnoticed by the sibling pair in the throes of their passion, Twilight’s horn was sparking and shooting fireworks… which meant that the inhibiting horn ring had come off, unlatched accidentally by Shining mouth as he nibbled and teased his little sister’s horn. Normally, this would have simply resulted in some magical sparks of energy…

But Twilight’s spell was all about utilizing the potential energy of alicorns… and by casting the swap she’d charged up the thaumic field… primed it like a rubber band, stretched too far. With the invoking of the field through her orgasmic casting, she had primed the spell to rebound, casting again and seeking out the nearest alicorn to swap with.

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Author's Note

Oh my.

Always so much fun to write Twilight-Shining... These two love each other so much. Throwing sticky, passionate, sibling-sex into the mix just ramps everything up to 11.

This is the first time I've done it from the Shining perspective... I really tried to add a layer of protective older brother... hopefully it comes through.

Now, which ending did you get? Don't cheat!

Who are we kidding you're gonna click on every ending you dirty cheater.

Gimme a like if you're enjoying... and comment on which ending you got!