Cookie was the first to start laughing, a giggling chuckle that turned the corners of Caisson’s mouth as well. All of a sudden, both of them were laughing. Forgotten was all the cloying anxiety of moments before, now a stream of warm, happy emotion poured from them — the happy rush of accomplishment after one faces one’s fears and leaves them behind.

Caisson somehow found himself in a supine position, his back lying on the warm hay-strewn planking of the Harvest family farm. His diaphragm bounced up and down with each guffaw escaping his smiling lips. This bouncing quickly made him acutely aware of where his sister had ended up after the tumble.

On top of his chest.

He looked down at her, laughing carelessly, tears of mirth also forming in her eyes as she similarly shuddered with delightful giggles.

Shudders that Caisson could feel.

In a very sensitive area.

While physics could be cruel, she could also be playful. The precise balances and momentum-changes of their fall had brought Caisson’s little sister, barely half his size and mass, to a soft landing laying right across his cock.

The soft fur of her belly and chest wrapped around every bit of his fat stallionhood shaft, sandwiching him between his own underside and hers. He could feel her body-warmth through the furry coating, her body rubbing along his sensitive nerves with each giggling bounce.

“I guess we’re both a bit klutzy.” She choked out, clearing the mirthful tears from her eyes. She looked down, bringing her nose-to-head with his half-flared head. “Well, would you look what I found, big bro.”

Caisson’s sighing grin became a moan of sensation as Cookie began to slide up and down on him, using her whole body as a biological chamois to polish his heavy log of stallion-flesh.

“Cookie…” Caisson managed to mumble again, his breath quickly being taken away by the pleasure from feeling his little sister’s body rubbed against him, running every little rib-bone and belly-muscle over the aching ridges and veins of his penis.

“Have ta’ use my whole body to handle you, big bro.” She looked up at him with a grin, her body still pressing into him, clenched by the arms she was wrapping around his barrel. “Although, maybe it would be better…” She bit her lip, eyes widening as that rougishtwinkle appeared in her eyes again.

Caisson felt her plant a sturdy hoof on his chest, just above where his massive cock stretched. Pushing down against him for leverage, Cookie pivoted herself upward, raising her upper body so that she was straddling him upright, one rear-hoof on either side of his barrel.

“Oof.” Immediately Caisson felt the previously distributed weight of his sister’s svelte body concentrated on one spot — where her butt rested on him, just below his medial ring.

She swung her other forehoof forward, bracing herself on his chest with both forelegs , looking almost like a cowpony might when saddled up on a bison — if the bison’s back was actually a supine, painfully-erect stallion, that is.

“How’s that feel?” Her mane was falling down from either side of her face, hanging down toward his face.

He’d never been under Cookie before. Hay, he’d never had any pony looking down at him for years now. Even though he could easily throw her off with his tremendous power and bulk, there was something appealing about having her on top of him. Something hot.

“It feels…” Caisson paused, being under Cookie wasn’t the only thing that was hot. He felt the place where Cookie’s body rested on him, the spot on his shaft just below his medial ring. It wasn’t just warm, like before. It was hot.

Boiling.

His gaze slid down Cookie’s body, from her cute little belly-button… along her slender lower-abdomen. She had a small set of nearly flat teats, pert little breasts that were perfectly-sized for a filly her age. On the peak of the cute pair of mounds was a dark nipple, painfully erect. Little eraser-shaped nubs that hinted at just how aroused his little sister truly was. His eyes continued downward...

That’s when he saw it for the first time — Cookie’s fillyhood.

The sparse tuft of fur just above her lips was sopping wet with arousal, the furry hair-strands slicked together in chaotic cowlicks from the thorough soaking they had received. Just below, the fur gave way to a set of plump, slick, lips. The bare skin was far darker than Cookie’s usual skin tone — almost black as Luna’s winter solstice, though they shone with a glistening wetness. Even as he watched, the dark folds throbbed from Cookie’s heartbeat, engorged with her life’s essence…

Her dark pussy-lips made the next feature stand out with stark, almost blinding contrast. At the crest of Cookie’s fillyhood, a striking flash of pink drew Caisson’s eyes — his little sister’s clit! He could feel the bit-sized lovebud as it pulsed out from her tight folds, slipping in and out with every other heartbeat, without ever retreating all the way back into its velvet cave. And with each pulse, the heart-shaped nub would slip along his shaft, touching his stallionhood and leaving a small, wet thread of honey behind.

And then, those dark lips were wrapping around his shaft-top, spreading so wide as to reveal the boiling-pink inner-labia of his little sister’s fillyhood, though they couldn’t cover more than a part of the ventral thickness of his cock.

It was like he was looking at a pony trying to wrap a dinner napkin around a redwood — it barely reached the halfway point.

“W-wet.” Caisson finally managed to fit his tongue back into his mouth after it had been hanging out in pure marveling appreciation of the sight of his sister straddling his dick.

“Mm-hm.” Cookie’s eyes were sparkling with that fierce hunger again. Her mouth slacked open, as she let a steamy breath slip over her lolling tongue. “I’m gettin’ a little… worked up… myself.”

“Y-yeah?”

“W-why don’t we… help each other?” she breathed, looking down at where her tight teen twat was straddled astride his shaft, before raising those ferociously hungry eyes to meet his face.

“Ok,” Caisson swallowed as much as answered. There was no way he could even think, let alone protest. He started to lift his arms up.

“No,” Cookie’s hooves moved from his chest to his shoulders, pinning them down. “I got this…”

Caisson nodded, heart pounding. Cookie was in control.

And that’s when she started to grind.

The sensation was indescribable. It was like a hot, wet, viscous, silk grasp sliding up his cock. Every bump and vein slid against her sex, eliciting shudders and whimpers from her as she continued to slide closer and closer to his face.

Both of them synchronized a grunt as Cookie’s clitoris bumped against his medial ring, forcing it to compress before it finally slipped over the prominent ring of stallionflesh, followed shortly by the furnace-like heat of Cookie’s pussy. Although she had already been leaving a sticky-wet, shining trail of filly-nectar in her wake, that particular bump had made Cookie follow her grunt with a squeak, a sudden humping of her hips… and a copious river of additional honey that spilled over either side of Caisson’s belly and dribbled onto the barn floor below.

But still, she kept grinding upward, inch by inch, pink on pink. She was approaching where the flat broadness of his ventral shaft finally started to narrow, giving way to the pronounced ridgeline of his corpus spongiosum, which put even more pressure on his little-sister’s pleasure-button as her slick lips began to slip around more of his tapering penis.

“Ahn… Ahn!” Cookie’s squeaks were becoming less intelligible now, her eyes alternating between closed and open, pupils rolling wildly. Her body was moving more erratically, pausing in its grinding journey to hump more fervently against his stallionhood, satisfying her insistent erotic itch and bringing the little filly closer and closer to a trembling conclusion.

That’s when she reached his cockhead.

The tapering flesh of his shaft, though still tremendously wide, blossomed out into the huge battering-ram that was his knobby head.

His little sister didn’t even hesitate; shifting a more weight onto her front hooves, she lifted her hips ever so slightly, clearing the almost cliff-like transition to move her grinding sex up onto Caisson’s flare.

“B-buck…” Caisson groaned a curse through clenched teeth as she ascended, feeling his sister’s love-bud grind against his glans, sliding its novel, slick-flesh, feel up and across his urethra — such a strange, yet intensely erotic act… and he was doing it with the filly that he’d been a big brother to for years. They were about to mash their excited sexual bits against each other with wild abandon.

And then she pressed against him.

Those wet nether-lips strained and stretched to slide over his hoof-sized cockhead, slathering his sensitive glans and flare-edges with soaking, sparkling sensation.

“Oh, f-fuck,” Cookie gasped. She was swirling her slick teen cunt all over his head now, as though it were some wet paintbrush and she didn’t want to miss a spot.

“C-cookie…” Caisson moaned in reply, resisting the growing urge to grab her by her hips and yank down. But he couldn’t resist the jumping pulses that were making his stallionhood jerk and bounce, each time releasing copious splashes of his own pre-ejaculate fluids.

“BC!” Cookie squeaked, tossing her head back and pushing down hard. Caisson could feel the filly’s inner-lips parting, stretching. The bulging protuberance of his glans was almost slipping inside her! It was so tight.

So impossibly tight. The angle was all wrong, her slipping along his head instead of on top of it — even if she was aligned there was no way her tight teenage pussy could admit his freakishly huge head. And yet there was no denying it.

His little sister was tryingto impale herself on his cock!

Caisson was in a state of disbelief. Cookie was trying to stuff his huge beast into her slender little snatch! His little sister, who he’d always known to be so cute, innocent, diligent. A beacon of good-behaviour, a filly he would ruffle the mane of and tease across the table. She wanted to fuck him, wanted it so bad she was grinding herself against his flare!

And he wanted it too.

His hooves dug into the floor, trying to find something to grasp as he resisted just throwing his sister to one side and pounding into her.

“B… BC!” Cookie’s squeaks were getting wilder and higher pitched as she started to thrust wildly into his flare.

“C-cookie!” He could feel his stiff urethral bump protruding into the forbidden tunnel just inside those tight inner labia, splattering his pheromone-laden pre-ejaculate into her body. So close! They were so close.

“Ah! AH! C-C… Caaaaaaaaaseeeeeee!” Cookie’s spine arched backward, curling like a broken spring winding up on itself, her head tossed backward, chin pointing toward the ceiling as her mouth fell open into a groaning scream of his name, Caisson, something she had never called him.

As Caisson watched, the wild spasm wracked through her body, a ripple of rising fur flowing to the extremities of every limb, even causing one of her hind-legs to kick wildly along his side.

And then he watched her delicate teenage fillyhood flower.

A powerful wink sent Cookie’s clit shooting outwards, farther than it ever had before, peeling back her marelips with potent contractions that squeezed and released in milking throbs, over and over.

And with each throb came a flood of steaming filly-juice.

Her humping hips seemed to pump even more of the oh-so-delectably fragrant nectar as it splashed all over his chest. His belly was soaked with Cookie’s fillycum — a hot, sticky mess of her perfume as she emptied her lubrication all over him.

Her orgasm seemed to hang for minutes before the clenching convulsions started to give way to a muscle-melting release, the added lubrication making her backslide down the long length of her brother’s cock as she melted away from her rigid, peaked posture.

“Ahnn…. Big brother…” Cookie’s contented hum as she slowly slid down him was but a tiny window into whatever pleasure cocktail was melting her neurons. Caisson had never heard her, or any mare sound so satisfied.

As she slid down him, he felt each bump she’d crossed on her way up, now kissed by her tight, athletic buttcheeks… and a strange kiss of hot flesh that he could only assume to be her hidden tailhole.

Inch by inch she slid back, mewing in post-orgasmic contentment the whole way… until she finally bumped back against his heavy balls…

Now painfully tumescent: Caisson had heard fromhis colt-buddies about the painful legend of ‘blue-balls’ (which always provoked a goofy joke from Hay Bale, who had blue fur to begin with), but this was the first time he was feeling that painful tightness in his gut.

Cookie’s little sister sat upright, resting her little teen butt on his heavy sack. He could feel the hot trickle of Cookie’s drooling fillyhood pouring over his balls, coating them in a layer of her sticky nectar.

“Ahhh…” Cookie sighed happily, still coming off her orgasmic-high. Caisson had to smile to himself — she looked so cute, so rosey with warm satisfaction: like some kind of sexual tabby that had been slipped a sack of cat-nip.

“Feel better?” Caisson grinned.

“Ahn?” Cookie’s face slowly reset as she roused and returned to herself. Quickly, her embarrassed blush returned as she realized her big brother was watching her. “Oh… y-yeah. Did you not, uh-?”

Cookie’s eyes scanned down, inspecting his stallionhood.

“Nope, but that’s OK,” Caisson sighed, reaching down and pumping himself a few times absently. “Sometimes I take a little longer to... y’know.”

“Now that ain’t fair, BC.” Cookie’s brows knit again, her tongue protruding from her lips as the fire in her eyes fanned back into flame. “Hooves off, BC. I got this.”

Cookie reached down with her hooves, slipping them underneath his heavy lower shaft, then starting to pull his girthy, massive stallionhood up, like she was erecting some kind of erotic, pink-flesh flagpole atop the Canterhorn. Inch by inch it swung up, faster and faster until it met Cookie’s chest with a meaty, wet, slap.

*THWAP*

“Celestia’s Mercy,” Cookie Whispered, looking down at Caisson’s monster against her body, “You’re right up to my ribcage.” The words escaped her in soft wonder — Caisson thought he was seeing a little bit of fear there as well.

“Y-yeah.” Caisson mumbled. The sight before him was obscene: his little sister basically hugging his sapling-tree-trunk sized stallionhood against her body, the tip coming up nearly two-thirds along her smaller body, as a wet patter of his pre-cum burbled into her chest-floof.

“You must be what, twenty inches? More?” Cookie chewed her lip, those eyes of hers flicking between an almost indecipherable mix of excitement and fear.

“I dunno.” Unlike many of his colt buddies, Caisson had never measured himself. He dreaded the confirmation of freakish size that the yellow tape would surely yield.

Cookie’s eyes flashed up to him. “You’ve never measured?”

He shook his head.

“Liar. Every colt measures.” She huffed, her hooves starting to slowly slide up and down his stallionhood, pressing his rigid shaft into her teats, then her belly, then her chest as she moved the force of her hug up and down his length.

Caisson’s mouth dipped open, surrendering to the sensations of having another pony... a filly... his little sister masturbating him.

“Hope Hammer said you were twenty-three and three-quarters long, and about eighteen around.” Cookie grinned, her hooves starting to move faster and faster. Long, powerful strokes that raced up and down his whole length as she pulled more and more of him into her body. “About as girthy as a barn-beam and longer than stud-spacing in walls. Hope’s special talent is carpentry, so all the fillies use her to compare the boys’ sizes at school.”

“Mmph!” Caisson groaned, the tightness is in his gut twisting tighter and tighter, like an overwound clock-spring, straining against its mechanisms. His whole stallionhood was throbbing, it had never felt like this. He’d never edged so close to orgasm then backed off at the last moment. This treatment was making him feel like his the pulse of engorged blood beneath his straining shaft-skin might burst.

“None of the other colts even come close, by the way.” Cookie smiled, her eyes simmeringwith desire. “I’m one proud little sister, because every filly knows that my big brother has the biggest…”

She pumped harder.

“... Meatiest…”

Another hard pump, her hooves working closer to his flare now, bumping and running along those glans and knobby ridges that were packed tight with sensitive nerve endings.

“... Sexiest…”

Swirling all over his flare now, urgently tugging his coronal ridge, pumping up and down with maddening, demanding, strokes.

“... buckin’ mare-splitting stud-cock!”

He’d never heard his sweet, innocent little sister use language like this. He didn’t even know she was capable of thinking language like this! It was so wrong — and so blazingly exciting! Her words were like a feral growl, like he was seeing the delicate outer disguise of Cookie stripped away — to reveal the lusting need she had as a mare underneath. For him.

Her big brother.

Her hooves had stopped pumping, grasping tightly now under his flare, squeezing him like a tube of toothpaste.

“And my big brother’s big fat pink cock belongs to me.” With this proclamation Cookie’s head dipped downward and her lips parted. Caisson watched, unbelieving. It was like time had slowed, an erotic trainwreck moving in slow motion as his sister’s burning blue eyes’ intense focus bore down on his drooling cockhead.

Her tongue slipped out from her muzzle just before it made contact, like a pony taking a huge, languishing lick of a dripping ice cream cone… and then he felt it: his little sister’s tongue against his cock.

Her pink oral-muscle started just below his throbbing glans, drawing up across his burbling urethra before sliding in a rough swirl across the remainder of his saucer-sized flare. And the intensity just ratcheted up from there — it was as if the first taste had made his little sister desperate for more.

Her mouth got closer, lips engulfing what little they could of his massive tip, suckling his throbbing cock-slit as her tongue ran wild, lapping against him with obscene slurping gulps.

“Oh FUCK!” Caisson grunted, his hips lifting up off the ground involuntarily. “Cookie!”

Cookie giggled into his cock, her humming laugh vibrating against his glans as she continued to lick her big brother’s flesh ice-cream cone treat. Her hooves started to softly pump once again, coaxing him as she attacked him with a novice’s enthusiasm: wild, uncoordinated licks and kisses that came faster and faster.

“C-Cookie!” Caisson grunted, meaning for it to be a warning. He felt something deep in his gut twisting, turning, breaking. That spring, so tightly wound, now starting to break and snap, about to release all its stored up potential energy. There was no stopping it now.

Cookie was just going faster, harder, more desperately. Her tongue was sucking right from the source of his leaking pheromones, and it was like she was a thirsty Saddle-Arabian fresh from crossing the desert at an oasis. Gulping and slurping.

And yet she still wanted more of him in her — he could feel her lips trying, futilely, to stretch enough to take in his whole stallionhead — an impossible task.

And about to become more impossible, as he felt himself begin to flare.

“AAAhhhnnnn!” The groaning scream escaped from Caisson’s mouth. His heart POUNDED out three consecutive beats, each feeling like he’d been kicked in the chest by an apple-farmer. Huge, heavy pulses of his cardiac muscle that drove massive waves of boiling stallion-blood through his arteries.

His cock throbbed, almost like a garden hose that had been plugged up, veins engorging and popping out as the surge of pressure flooded through his pink cock, turning it a dark shade that was almost red.

It reached his flare, ballooning out the already huge knob into something terrifying. Cookie’s eyes shot open as the stallionflesh in her hooves expanded and bulged, blooming wider and wider as her brother flared.

“Mmmf!” She gripped him and pulled him tighter against her mouth as more of his tip grew away from her capacity to hold it in her muzzle, leaving her just pursed against his urethra. Holding on for dear life.

“Ohhh F-F-UuUuuuuUuCk!”

The spring snapped.

Caisson felt his heavy, buck-ball sized testicles shoot up toward his sheath, smushing against his sister’s bottom as they retracted. A hedonic wave of overwhelming testosterone and potent neuro-chemical pleasure raced up to his brain where it exploded like fireworks on Midsummer’s Eve, flashing through his cortex with crackling sparks of pleasure that triggered a euphoria that he’d never experienced.

His thaumic system throbbed, ancient earth-pony magic energizing his every limb and muscle, bulging and powering muscle fibers and skeletal structures with powerful intrinsic life-giving vigor… including his sexual system — stirring the deep, primordial, biological advantages of the prolifically reproductive earth-pony race… flicking the hidden light-switch of the prehistoric alpha-stud harem-leader of Equus’s feral pony herds to on.

And then he came.

The first burst of stallion-batter blasted out of his cock, right into his little sister’s throat. A thick, carpentry-glue-like, rope of his steaming cum shot right into the back of her throat. The pulse lasting seconds as it emptied out of him.

Cookie’s cheeks quickly puffed out comically, like a squirrel holding too many nuts, as she was never going to be able to swallow her brother’s ejaculation fast enough. Finally, her lips cold hold no more and they burst the seal from his angry flare, spilling a deluge of frothing cum that spilled down her chest and his shaft.

She pulled her mouth from the throbbing cock, leaving an erupting jet fountain of splashing stallion-batter shooting up into the air, landing in heavy, sticky lines all over her mane, her shoulders, her chest.

Finally, the fountain cut off, tapering down.

“AHHG!” A second grunt, a second thrust of the hips. Caisson’s second spasm began.

Caisson saw his little sister flinch away, but still receive nearly a full on splatter of his second ejaculatory spasm, hitting her right with such impact it was like a paint-filled water balloon bursting on her. The stream of gushing cum was like a firehose against the underside of her chin, splattering off of her to cascade down in sheets of splattering cum to slather her belly.

“Ahh!” A third shot. Just as hot and thick, this time up in the air as Cookie had managed to push her brother’s exploding, mammoth, stud-rocket away from her. Lazy jets of Caisson’s potent seed flew up to splatter down on her mane, on his chest, all over them.

And then a fourth, and a fifth, all while he bellowed like a charging buffalo.

Caisson felt like his whole essence was being drained through his penis, pouring out volumes that he didn’t even know he had. He sometimes had big loads, if he had abstained for some time… but he’d never cum so hard before, with such clenching, powerful spasms.

Cookie was almost laughing now, playing with the rock-solid stallionhood in her hooves like it was some water-park cannon, directing it at different parts of her chest to coat her light-colored belly fur with her big brother’s genetic paint.

An eighth, a ninth. His voice grew rougher, his vocal chords strained from overuse, pleading for the torrents of cum searing from his cock to subside. A glob attached itself to the ceiling, suspended by gelatinous surface tension only to come tumbling down.

The shots were starting to lose just a touch of their intensity now, the streams not arching so high, the cream coming out thicker and more solid. Through squinting, burning eyes and with clenched teeth, Caisson watched Cookie sometimes direct a spasm into her open mouth, taking it on her tongue for as long as she could before having to direct her jerking cannon away once again.

A final, tenth spasm… dying down to a trickle that slid down the underside of his stallionhood.

“Aahh… hah… hah…” Caisson’s orgasmic aftershock began to relent, the spasms dying down and leaving strange ripples in their wake. And yet, something seemed wrong.

There was no happy, contented wave of pleasure that usually came after he climaxed. His heart was still pounding, perhaps even harder than before. His stallionhood, which usually softened quickly after a hoofing-off session, was still stiff as an oak-tree… maybe even harder than it had been before he came.

He buzzed with an energy through his every muscle.

“H-holy buck, BC.” Cookie half-chuckled, half groaned. She was working her hooves along her chest, trying to clean the absolutely cum-soaked fur. “Were you backed up or something?”

Caisson looked at her. Dripping in his seed. For the first time, he didn’t just see his little sister. This was a filly. A mare.

How could he have not noticed it before?

“Goddesses, you’re incredible, BC.” Cookie sighed, letting a hot breath escape her muzzle. As she wistfully looked at her stained, drenched body. “I just love your smell. Your taste. I don’t know why… its just so comforting… so stallionly.”

Caisson’s nostrils flared, as he listened to his filly talk about him. He could smell her. Drenched in his scent… but underneath that, was her. Her musk. That cinnamon-sweet spicy perfume that was coating his balls, that this sexy little minx had been flicking to and fro since she’d stepped into his territory.

She was in heat.

His filly was in heat.

How could he not have noticed before?

“Oh BC.” Cookie cooed, grasping his cock again with her hooves in wonder. “Wow. Just wow, and you’re still hard?”

And now she was touching his stallionhood. Playing with him. Wanting him.

“I love you, BC.”

A rumbling nicker escaped from his mouth as he surged upward, easily tossing Cookie backward in a tumble off of him as he stamped up to his feet.

“B-big bro?” Cookie looked up at him from her side, on the ground.

She wants me. She needs me. My filly. And I need her.

He stamped hard, letting out a whinney as he did so, standing stock straight. Now he was towering over his little sister, his huge, draft-horse sized bulk easily twice her size, huge muscles rippling and bulging along his barrel, his whithers, twitching through his flank and his neck.

He was in rut.

Author's Note

Oh.

Oh no.

Hold on for dear life, Cookie!