Cookie was suspended in mid-air, hoisted up by Caisson’s massive stallionhood.

“Ahhh!” the filly’s hooves pawed and paddled at the air, making her look like some bedraggled puppy being held over a bath.

Caisson turned slightly, as he considered whether to take his new broodfilly prize to somewhere more convenient to rut her… swinging her underneath him while she was fully lifted by the sheer power of his stallionliness and the rigidity of his cock as she rode his belly. A few clopping steps brought her over to a nearby interior wall, used to separate off the part of the barn used for tools and storage from the side used every day — it was perfect.

He drove forward, finally allowing his sister to brace against the wall with her forelegs as he lifted himself up to a standing position himself, his huge forehooves reaching much, much higher on the cedar-planks. They were both standing on their back hooves now, in a perfect position for him to really start to buck.

“Ahn! AHN!” Her first moans came as Caisson started to pivot his hips, sliding an inch back and forth into her body, grinding against every nerve in her completely-stuffed pussy and bumping over and over into her cervix as he did so.

It was a slow rhythm, his balls softly swinging back and forth, and Cookie moaning and clenching, getting used to the powerful but laconic pace as he began to pump in and out of her, each stroke inducing a groaning exclamation. Manageable by the brave little filly...

At first.

He began taking bigger outstrokes, pulling further and further back with each piston, using his rump and legs now instead of just the tilt of his hips. First two inches of his bright-pink steaming cock slid in and out of Cookie’s dark lips, then three, then four.

“Ahn!”

*PLAP*

“AHN!”

*PLAP*

A new sound was filling the air — the muffled impact of his heavy stallion-sack swinging back and hitting the inside of his own legs as his increasing momentum started to cause them to
move through the air like a pair of shotputs hanging in a leather bag off a pendulum.
*PLAP*

“AHN!”

*PLAP*

Harder and harder, faster and faster. Each time battering his throbbing cockhead against the deep, unyielding barrier of her cervix. Their flesh was melting together now — those subtle, swirling folds of her fillyhood and the pulsating veins of his stallionhood. It was like they were becoming one body, their cacophony of wild motions and clenches and violent love-making forming some singular lust-depraved creature.

*PLAP* *PLAP* *PLAP*

“BC!”

His thumping, pounding rhythm was faster now, each thrust bumping his sister’s head against the wall, making it sound like somepony was knocking insistently on a door.

He could feel her orgasms as they came in waves, their flesh-union making it feel almost as if they were his own. Milking convulsions of her vaginal muscles and humping flexes of her body rippling through him, as his inner-thighs were whisked with her thrashing tail… before being coated with squirt after squirt of her sticky filly-spray.

His stud-brain was still in full control, running its primitive calculations. It judged his choice of mate positively: his brood-filly was a tough, courageous one. A worthy mother for his genes. She was thrusting back into his cock now, pushing backward with her hips to take as much of his monstrous masculinity that she could.

*PLAP* *PLAP* *PLAP*

“Yes! YES!”

He could feel the hard press of the wooden wall against his stallionhood through his sister’s body — her belly bulged from his penetration grinding against those planks as his rough force sandwiched her. She was literally entirely stuffed with HIM, his lusts, his desires, his overflowing rut… his cock.

She was giving her all.

And he still wantedmore. Needed more.

He could feel the spring in his belly winding, metal under tension that hummed with built up potential energy, ready to snap and explode. His orgasm was close, a thick voluminous genetic payload that would forever claim the destiny of his brood-filly and secure their progeny. But his wild, ancient instincts demanded that he deliver his essence as deep and effectively as possible — he needed to empty himself into his filly’s womb.

*PLAP* *PLAP* *PLAP* *PLAP*

Harder! HARDER!

His muscles surged forward, pounding his little sister into the wall with the force of a hoofball linebacker, making the planks groan and shudder. Great, steaming gouts of fillycum and other obscene fluids splashed backward, extracted by the piston-like action of his plunging stallionhood, and still he slammed against the impossible barrier of Cookie’s cervix.

*PLAP* *PLAP* *PLAP* *PLAP*

WHY WON’T SHE LET ME IN?

Caisson started to bend his gasping, drooling mouth down toward his little sister’s lashing neck. A spot just before her wildly flowing mane looked particularly vulnerable, a soft nape of skin that might just be the final additional bit of leverage that he needed to ram himself into his territory.

As his teeth dug into her soft fur, he could taste the sweaty froth building up there, the salty exertion of his filly’s body the coating sheen of her exhaustion matching his own in their frenzied, pounding rut.

“OHHHH, CASE!” This was a feral growl, like some giant jungle predator, barked out with the volume of a scream but the baritone of a rumbling moan. Cookie’s head twisted to look at him. Her wide-eyes were filled with passion and fear, excitement and adrenaline. She was smiling with the dopey grin of a stumbling Berry Punch, even as her own teeth snapped dangerously at him.

They weren’t brother and sister, crossing a forbidden taboo-line to fuck each other lovingly in their family barn.

They were two young horses, earth-ponies in complete rut and estrous, having entirely succumbed to the wild, primeval neural pathways and thaumic forces that evolution had left in their modern pony-bodies.

*PLAP* *PLAP* *PLAP* *PLAP*

Cookie’s gnashing teeth and head were quickly followed by a small bucking kick… which made Caisson’s rear hooves slip as they took on all of his sister’s weight at an awkward moment in one of his plunging strokes.

Suddenly, the barn wall was bearing all of their weight at the precise moment that Caisson’s heaviest thrust slammed into his little sister’s hips. A rending crack joined the wet slapping sounds filling the barn as the cedar planking of the wall groaned and bent — before snapping in two.

*WHAM* *CRACK*

Caisson had just fucked his sister through the wall.

After the one plank broke, they all began to fail, one after another in a huge, chaotic collapse. Timber, nails, hay, and ponies came crashing down onto the other side of the interior wall. Cookie’s body came tumbling under her big brother’s, who managed to ride the small-scale building demolition down, landing on all four hooves right on top of his sister. The smaller filly had slammed bodily onto her chest, front legs splayed out in front of her and her head against the ground.

Her rear end was still suspended in the air by her stud’s rigid, throbbing-pink penis — leaving her face-down, ass-up in a position that allowed her big stallion to bring all of his force to bear against that final stronghold.

That final, pistoning thrust that had rent the very structure of the barn continued on through the fall… bringing the full force of all that horse-muscles plus the momentum of its weight bearing down in one, ultimate movement.

*SPLAP*

Caisson’s huge testicles swung forward at the same time, slamming into Cookie’s teats and sending out a spray of filly-nectar from the coating that had slicked its surface.

“CASE!!! AHHNNNnnnNNNNNgh!” Cookie’s orgasmic growl reached a new crescendo, more like a screaming squee. She turned her bright blue eyes up to look into his. Those beautiful irises shifted, morphing... quickly forming into a pair of heart-shaped irises that throbbed and pulsed with intensity.

He could see at that moment, his little sister’s complete and total transformation. Her mind, her heart, her spirit… they belonged entirely to him and his masculine studliness now. This was truly his special talent — he was an alpha. And his sister was the first to fall entirely to him.

Deep inside her body, he felt his huge, throbbing flare press into that impossible opening. Only some divine intervention of the Princesses, or more likely some lingering earth-pony magic ability would have ever permitted his gigantic girth to penetrate her cervix and enter her womb.

And yet it did.

Caisson’s throbbing flare slipped into that final bastion of his little sister’s deepest, most feminine refuge, the life-creating factory so sacred and wondrous and feminine.

“...HnnNnh*GAH*ghhHHHH!”

And it slammed against the far end of it, driving a bulge into Cookie’s diaphragm that interrupted her moan with a hiccup like gulp.

Caisson’s perception was razor-sharp, his mind drinking in the details of every nerve fiber even as it overloaded his cortical circuitry. Cookie’s whole body was in a state of ur-orgasm. Her heart-eyes danced and dipped wildly, an indication of the wild wash of endorphins, neurochemistry and magic melting her pleasure centres. Her whole buddy pumped and gyrated up against her brother, trying desperately to stuff the final few inches of his cock into her body and hilt him, despite the fact her body had literally no more ground to give.

Each gyration was in perfect synchronization with the involuntary, milking clenches of her whole vaginal tunnel. Every muscle in her body was cooperating to create powerful, suckling grasps of those vaginal walls… heavy strokes that would have put a seasoned milkmare to shame.

He trembled as her womb expanded and thrummed, preparing to receive the estrous-sating load it had been so desperately demanding for so long.

He could sense that the whole of her mind, body, and soul was begging for her brother to join her in the forbidden, terrible consequence of culmination.

Everything in her wanted him to cum.

Fill her.

BREED HER.

And he did.

The pulse of pleasure was sudden, like a gunshot. For a moment Caisson wondered if he had been struck by lightning, or if some tendon or muscles had torn in the fall. The surge of pure testosterone raced from his hind-brain, washing down through every one of his arteries and veins, igniting every nerve filament on its way; a branching bolt of overwhelming sensation that accompanied the instruction from brain to balls to fire.

His balls shot upward, the clenching muscles of his powerful abdomen pulling them in tight as they swelled with a rush of magical energy.

His flare, already fully-expanded, managed somehow to grow even wider. The blossoming plate of stud-flesh thickened, the knobby bumps in its edges embedding themselves into Cookie’s womb-walls, firmly lodging the hoof-sized hunk of flesh in place.

A throb of swelling flesh raced down his length, like a cartoon-hose bulging after being connected to a fire hydrant.

His urethra thickened to the half the size of a bit, opening wide from the pressure of the release, screaming up his shaft.

And then he exploded.

The first blast of boiling, fertile stallion-batter shot with enough force that any pony watching would have seen a bump appear on Cookie’s underbelly. Heavy, glue-thick cream splattered and swirled out of him, an unending, unremitting flow that lasted for seconds.

*PLAP* *PLAP*

“YesSss… YesSSsShhh!” Cookie’s moanings were made nearly incoherent by her hanging tongue, and the sound of soft thuds of her flanks against his cock as she humped back onto his rigid, jerking stallionhood. She was impaling herself onto his orgasming penis, delirious with the joy of the heat-sating potion gushing into her.

Within the first few seconds, his gushing stud-cum had filled his little sister’s womb — the boiling body heat of her internal body temperature keeping the creamy slurry a frothing liquid as it topped off her uterus — then began to expand it.

*PLAP* *PLAP*

“Unhhh…….”

The second blast followed right after the first. Heavy wracking spasms of stallion muscle that squeezed with coordinated force to wring out every drop of semen, each one swimming with life-creating sperm. The little filly’s womb was getting packed — the seal of her stud’s flared head inside her plugging any possibility for escape, causing the pressure of the hot, frothing cum reservoir inside her to rise.

*PLAP* *PLAP*

A third shot. Then a fourth.

Each one seemed to last just as long as the one before it. Impossible amounts of stud-essence were being generated and injected into his sister. Only some arcane combination of special-talent, genetic lottery, and earth-ponic magic could be responsible — already Caisson had produced a milk-bottle’s worth of volume without any hint of tapering.

*PLAP* *PLAP*

“G-Guh… Goddesses!” Cookie squeaked out, still clenching and climaxing around her big brother’s orgasming cock, “It’s… too much!”

Caisson could hear her, but it didn’t mean anything to him. He had been flooded with so much oxytocin and dopamine that even his instinctive drives had begun to burn out. Everything was just pure, searing pleasure now.

He felt like he had merged, melted into his filly, becoming a single organism.

There was no ‘Caisson’ anymore. Just flesh and feeling… a grunting, heaving sensation of emptying.

*PLAP* *PLAP*

As his sixth blast stuffed the overly packed filly, her belly began to expand outward. Subtly at first, a barely noticeable bump in her abdomen — but now that her body had begun to stretch, it came faster and faster… like a water balloon held under the sink faucet.

*PLAP*

“Ahhnn… ahnnn!” Cookie’s moans were coming with each orgasmic burst from his still-emptying balls now. The blasts slowing in frequency but not intensity, and each one growing the once-small taupe lower belly larger and larger.

Already it looked like the teen was four months with foal as her cum-belly began to push against the tops of her teats.

*PLAP*

Slowly, dimly… Caisson’s mind was coming back. He was ascending from the depths of the little-death toward the light of consciousness. The dark edges of his vision swam with photopsia-flashes as his brain began to reboot, pathway by pathway.

*PLAP*

“Mmmnh! Mmh…” Cookie’s belly was obscene now — nearly touching the barn floor, and pressing up against her lower ribs, as her womb accommodated the tenth blast of piping hot cum from her stud’s ridiculously potent reproductive system. If Nurse Redheart had a look at her she would have prepped a midwife for an immediate delivery… this filly was eleven-months pregnant, possibly with twins.

*PLAP*

“Cuh… C-Cookie?” Caisson groaned, his head throbbing.

Where was he? What was he doing?

He felt another incredible release from his cock, which felt so painfully full and yet so wonderfully gripped, in something so massaging and tight and…

Oh Goddesses, he was cumming inside his little sister!

He felt his stomach drop out from him, a sudden surge of guilt, panic and terror.

What had he done!? How was this happening?

Instinctively, he began to jerk back, only to find that he was lodged inside his little sister. He’d never felt so huge, so engorged, before… there was no way to back out of this. He felt a strange mixture of release and shame as another shot raced out of him, knowing that it was stuffing his little sister’s body, that he was creaming her.

*PLAP*

And she was humping into him!

“C-caisson… I…” Cookie groaned out, looking up at him with heart-shaped pupils. Her mane was bedraggled, drenched with sweat and other fluids, little twitches in exhausted muscles making her quiver and whimper. She’d given it her all. “I… love you, big bro.”

Caisson felt his heart melt. That was his little sister.

His precious little sister.

She loved him! And dammit if he didn’t love her too. Not just some pleasure-mare, some buck-buddy or a worthy target of an accidental rut: his sister.

The initial wave of guilt began to slide away, replaced again by the wash of post-orgasmic chemistry that could bind two hearts so closely together after the tumultuous chaos of sex.

He would be there for her, always. And that meant now, too.

*PLAP*

This time it was Caisson pressing down into her, a gentle, soft thrust meant for her. Not him.

“Shh…” Caisson cooed, carefully lifting a hoof to stroke his sister’s mane. “I love you too, sis.”

*PLAP*

“Mmmm…” A contented sigh-giggle escaped from Cookie as her loving big-brother loosed his final cumshot into her body.

*POP*

Her belly-button popped outward, turning from an innie to an outtie, her cum-stuffed tummy rumbling with contentment.

“C-case…please...” She whined, blinking up at him, dipping her eyes and pursing her lips. The tone reminded him of when she would beg for ice cream as a foal.

“It’s all gonna be OK, Cookie.” Caisson smiled, leaning in and planting a kiss on her lips. He didn’t know how to kiss, this was his first. He’d kinda put the cart before the pony there. There would be no Prench-kissing, no slobbering and necking. The peck of his lips on hers, brother to sister, pure love… was more than enough.

Her tense, spasming fillyhood, exhausted… finally seemed to relax. Both of them were coming in for a soft landing after what felt like an eternity of strenuous hyper-stimulated climax.

*SCHLORP*

“Ahn!”

A combination of Cookie’s relaxing filly-muscles and Caisson’s ever-so-slightly softening stallionhood was just enough to create the tiniest of gaps breaking the seal of flare to uterus. With the force of the emergency spillway of Ponyville dam being opened, a huge waterfall of burbling, thick, glue-like cream began to squirt from the tight junction of Cookie’s outer lips and Caisson’s still-girthy base.

“Shh… shh…” Caisson whispered, stroking his sister’s mane and resuming their gentle kiss.

*SCHPLAP* *SCHPLAP*

Caisson moved his hips gently, slowly. The wet, soaking sound of his humps mingling with the content hum of their smouldering kiss.

“Mmmmnnn… big bro…”

“Cookie…”

*SCHPLAP*

Carefully, Caisson rolled off his aching legs onto his side. He was still embedded deep within his little sister’s belly. Though it wasn’t quite as plump as it had been before, she was still looking quite pudgy as they both lay side by side in the growing puddle of his out-spilling semen amidst the wreckage of their earlier wall-breaking union.

*SCHPLAP*

They were comfortable now, spooning each other, and slowly, gently bucking. Soft, tiny strokes accompanied by the wet schlorps of his fertile batter being plumbed from her. There wasn’t the insane, heightened passion-inferno of before, but their happy, slow-fuck burned just as hot. They stared into each other’s eyes, content to live in just the moment.

Perfect.

It was perfect.

Caisson could have lived there forever, with Cookie. What else mattered than this feeling? Of loving and being-loved so completely? Did the outside world even ex-

...

“MOOOOOOOOM! CAISSON AND COOKIE ARE FUCKING IN THE BARN!”

Caisson watched as Cookie’s eyes shot wide in fright and alarm, like she’d been doused with a bucket of cold water.

Posey.

Their baby sister.

Standing in the open barn door, from where she could see everything and calling back over her shoulder. She must have just arrived from grade-school! Their mother would be meeting her to harness the blank-flank filly up!

“P-posey, you little ratfink, shut up!” Cookie half-squeaked, half-screamed. She surged, trying to stand up, only to find Caisson’s still-embedded stallionhood preventing her.

“Posey, language.” Golden Harvest’s voice drifted through the door, getting closer.

“It’s TRUE, Mom. And they even BROKE A WALL. You guys are in big trouble, now!”

Caisson watched, terrified, his hooves unable to move as his mother appeared in the doorway. There was no chance to hide, no way to explain the fact his mammoth, big-pink-cock was embedded in his little-sister’s cum-fattened belly.

All he could do was pray to Celestia.

“What are you going on about young filly? Oh. Oh!” Golden Harvest looked at her two eldest children.

“H-hey momma…”

Author's Note

UH OH.

Dammit POSEY, you little BRAT!