“Uh, rear.” Caisson liked his belly-band to be as comfortable as possible - he always found that having a snug fit in-front and in-behind it before snugging it down to help with that.

“Mhm.”

As she turned, Cookie’s tail brushed against his left shoulder. There was something lingering in the air behind her. A hint of something he couldn’t quite place - cinnamon? Cookie wasn’t one to wear perfume, though. The smell lodged in his nostrils and to the back of his throat like a sticky mist; everywhere it touched seemed to grow hot and tickly inside his mouth and nose. He scrunched his nose up and opened his jaws as he lifted his head toward the ceiling involuntarily to attempt to clear the cloying scent.

What was that?

“H-hey!” Cookie chirped, tapping him on the flank and making his head snap back to attention. “Ready?”

“Yup.”

“Spread ‘em out a bit so I can see better, never harnessed a stallion before.”

“You strapped me up back in the day.” Caisson reminded her.

“You were more of a... colt back then.”

“You never helped Dad out?”

Cookie shook her head. “Naw, you know most of the time he’s on magic duty. And whenever he does need to pull something he’s pretty fussy that only Mom set his straps.” She clicked her tongue then shot Caisson a pointed glare. “Now quit stalling and let me see what I’m working with, BC.”

Caisson blushed a bit, despite himself. Why does this feel so weird? Why is my heart racing? Slowly, he stepped his rear legs about two hooflengths wider than his resting stance, as if he were digging in before trying to yank a stump out. She’s seen me a hundred times since I’ve had my growth spurt, how is this any different?

But it was different. Whether it was that smell in the air, the tight proximity of the two, or the way Cookie’s eyes seemed so intently focused on his butt… this was exciting.

“Tail too.” Cookie complained. “Sheesh, you’re acting like a blushing bridesmare.” But Caisson could see the intensity in her eyes — did she want to see?

He lifted his pewter-gray tail and moved it to one side, further than he even needed to - enough to even show his tailhole. There was nothing between his rump and his sister’s eyes now.

He watched as Cookie’s eyes flashed wider, more than a casual reaction. The blush on her face seemed to flush all the way to her eartips. The filly’s mouth fell open slightly for a half moment and Caisson swore he started to see his sister’s white tail start to rise above her rump.

Then she suddenly slammed her rear down against the barn floor into a sitting position, hiding it from view.

All he could see was her make the strangest wince for a moment, one eye contracting slightly as she bit down on her lip — as if somepony were plucking a splinter from her frog. He could see the end of her tailhairs behind her as they swished on the barn floor once or twice, then the moment passed.

“You OK? W-what was that?” Caisson asked, tilting his head.

“N-noth- *ahem*” Cookie’s voice had first come out as a croak, necessitating her to awkwardly clear her throat and thump her chest with a forehoof. “N-nothing.” She folded her ears backward against her skull. “Just a cramp.”

“You sure?”

“Yeah, BC.” Cookie swallowed again. “Just give me a second.”

Caisson watched as his sister did the weirdest little shuffle, wiggling her butt against the wooden floor of the barn a few times in a way that reminded him of when the family collie had an itchy backside.

“W-what?” Cookie shot at him, unable to meet his eye.

“Nothing.”

“Ahem.” She cleared her voice again, patting her breast then let out a steadying breath and stood back to all fours.

Caisson’s nostrils flared as she rose. Whatever that hint of a smell had been before, it was filling the barn now. Every breath he took was heavy with that strange cinnamon musk, hanging thick in the warm air. Not that he disliked it — with each breath he would swallow, as if he could actually drink any of the mysterious perfume that had condensed in his muzzle.

He felt something in his gut twitch, a little shiver that roiled into his groin. He quickly gritted his teeth, and tensed his abdomen. He had a sneaking suspicion if he didn’t clench up a bit he might drop right then and there.

“You, uh, certainly got bigger since the last time I saw you.” Cookie interrupted him, flicking her eyes up at him as he looked over his shoulder at her. Caisson saw her ears slowly tilting back up with growing confidence before she cracked a grin. “I remember ‘em being a lot smaller.”

She’s talking about your sack!

“H-hey now, ain’t nice to tell somepony they’re packing on pounds in the rear.” Caisson nervously joked, trying to pretend she was talking about something else.

“Pft.” Cookie scoffed, stepping up as her grin became sharper - her muzzle was almost level with the organs in question. “Last time I got a look at ‘em they were like a pair of acorns, but now these are more like a couple of buckballs in a leather pouch.”

As she said these, Cookie’s left hoof reached under and lifted his right testicle, as though it were the most natural thing in the world. Caisson’s heart skipped a beat, a surge of adrenaline and excitement pouring through him as he felt his sister’s soft frog, her delicate underhoof, press against the slick skin, hefting him and feeling his weight.

“...heavier than one of ‘em though.”

She’s touching me… down there! Caisson’s mind popped with shock. He wasn’t sure why he was getting so excited by this, he knew that lots of touching could happen when somepony was harnessing up. But even his mom hadn’t just… fondled him like that!

“Don’t they bug you? Bouncing around against your leg?” Cookie asked, even as she moved his sack carefully up and to the right, slipping a quarter-strap along the inside of Caisson’s left inner thigh. The thinner, lighter straps were used to keep the larger britchen strap that ran across his buttocks in place — especially with a temporary harness like Caisson’s, these were needed to keep the critical larger strap from sliding up and down.

But they certainly ran right extremely close to some very fragile equipment.

Colts nicknamed them ‘gelding-straps’ for a reason: if you got a bit of your junk pinched when hauling in to tighten up the britchen… a common joke was that the Canterlot opera could always use more male altos. Still, the amount of movement and holding that his little sister was doing to take care and give proper clearance seemed excessive.

“Uh… I… not really. As much as any stallion I suppose.” Beads of sweat were popping out on his forehead - he couldn’t clench much longer.

“But yours are so much… bigger.” Cookie squeaked, as she shifted her hoof across the underside of his pouch, carefully taking hold of his right orb and moving it out of the way of the right breeching strap.

“Really? Hadn’t noticed.”

“Sure - Dad’s not this big.” Cookie remarked. “The mares around town say you’re even bigger than Big Mac in his prime.”

“They talk about my… uh… tackle?” Caisson hesitated to use other terms with his little sister, hoping to preserve her innocence. It was hard to reconcile that innate desire to be a protective big brother at the same moment she was groping the tackle in question, while informing him it was apparently a source of town gossip.

“Your balls?” Cookie giggled. “Sure, though I gotta say, up close they’re even more impressive than I’d heard.”

“C-cookie…?”

“Sorry, sorry.” Cookie quickly interjected before he could scold her. She held up a hoof by way of apology, letting his dangly bits come carefully to rest in their black smooth-skinned coin-purse. “I ramble a bit when I get nervous.”

Caisson let out a little breath, finally able to release a bit of the clenching tension he’d been using to suppress dropping. “Why are you nervous.”

“N-nervous?” Cookie blushed, her ears folding back. “I… I’m not nervous.”

“Then why did y-”

“Anyway, crupper’s next.” Cookie hustled quickly, avoiding his question.

She was pretty nimble at threading his tail through the crupper-loop and drawing it up under his dock. The leather-covered loop slid up his taint, bumping over his tailhole and then settling comfortably against the notch of his dock. Caisson shivered when the loop touched his backdoor: he was always a little nervous about it, and showing such a private area certainly didn’t make him any more comfortab—

“Boop!” Cookie’s hoof poked him right in the middle of his pucker.

“Gah!” Caisson barely suppressed the urge to instinctively kick backward, but he couldn’t help but stand stock straight, a shiver rippling through him. This also had the effect of getting him to release his spartan-like tensing of his lower abdominal muscles.

He felt himself start to slip from his sheath, the flesh pouring out from inside him like some sort of meat-slinky. It was impossible to stop dropping once it had started, only slow it down. His only saving grace was that Cookie couldn’t see it from her angle.

Yet.

With the bellyband still to go, avoiding giving his little sis a face-full of ‘little Caisson’ was no longer an option. He only had one hope now.

Don’t get hard. Don’t get hard!

“H-hey!” Caisson choked out, as soon as his mind had set on the new gameplan. “What’s the big idea!? I nearly kicked the teeth outta your head, Cookie!”

“Pft, hahaha!” Cookie laughed mirthfully. “Sorry BC, couldn’t help it. Mom said you were touchy about your butthole, I had to pay you back for all the teasing you’ve given me over the years.” She stuck her tongue out at him playfully, without any of the malice of a real tongue-out rebuke.

“Yeah, well… let’s see how you like it if I poke your tailhole when I’ m strapping you in!” Caisson harumphed, grumpy that a stupid prank had ended up overcoming his efforts to keep himself tucked-up.

“Pft, I don’t care.” Cookie waggled her head tauntingly. “I ain’t a delicate flower like you. Won’t bother me if you prod my ponut.”

The words took a moment to process in his mind, but when they did — a flush of red crept over his face and his eyes bulged.

Cookie noticed, her blush deepening as well.

“N-not like that!” She shouted immediately. “That’s gross!”

“I didn’t say anyth-”

“I ain’t that kind of filly! You’ve been spending way too much time with those depraved city-colts!”

Caisson had heard rumors from several farmers of both sexes which disproved that the orifice in question was only the fantasy domain of depraved city-colts. But this was not the time to bring up those rumors. How did I get into this situation with my sis, anyhow?

“I’d never imply tha —”

“Just drop it BC,” Cookie harumphed. “You better not poke me there, dummy.”

Caisson just vigorously shook his head in agreement, keeping his mouth shut.

“Ok then.” She sighed, stepping back and nodding. “I’ll tighten your breech straps then— ah.”

Ah.

She was standing stock still, on his left side. Her big blue eyes wide and locked on… him.

He wasn’t completely dropped out of his sheath yet, but there was no way what was out could escape notice. And she’d never seen him like this: there was a difference between a ‘little’ drop like a colt might do to take a leak — something she’d probably caught the odd glimpse of here or there.

But this was one of those drops that happened before springing into a rock-hard stiffy, where a stallion’s body would completely relax and let every bit of phallic flesh hang-out for all to see.

Inches upon inches of pink Caisson meat arched droopingly toward the barn floor. The damn thing might already have been touching the ground if it didn’t have just enough blood pressure in it to give it a lazy, floppy curve as it extended further.

“Ah.” Cookie repeated. The curt phrase made Caisson think that maybe she was stunned into a brain-reboot of her own.

“S-sorry.” Caisson apologised.

“O-oh?” Cookie tilted her head, turning back to him then shooting a very nervous smile. “Oh! Oh don’t. Don’t apologise.” She laughed, not the mirthful giggle of earlier, but a nervous chuckle to conceal fear and embarrassment. “It… it’s normal, you know. Dropping.”

“Y-yeah.”

“Mom said it happens.” Cookie rambled quickly, words tumbling out one after another. “Just means you’re relaxed is all. Means I’m doing a good job and you’re comfortable letting your muscles unwind.”

“Y-ye—”

“Doesn’t mean that you’re doing it on purpose. Or that it is for sex. L-like an erection, I mean. Could just be you’re mellow and calm.” Cookie’s words seemed to be going even faster as she went along, her eyes nervously darting between Caisson’s face, then back under his belly. “Mom said that, if it happened, just ‘cuz it’s out doesn’t mean that you’re getting a hard-on for me.”

“N-n—”

“Not that I’m saying I’d be angry if it was. Um, a hard-on. For me, I mean.” She was completely stream of consciousness now, words bumbling out of her lips in fumbling futility, her embarrassment growing moment after moment. “Mom said it isn’t a big deal even if it was. Just a compliment. A nice compliment for a filly, is all.”

“C-cookie, I—”

“So, thanks for the compliment! If it is one, I guess. Don’t mean to imply. Compliments are nice. It’s nice. I should give you one too; that’s what Mom said. ‘Stallions are proud about their penises!’

“I—”

“Not that I’d give you a fake compliment! Y-your stallionhood is nice! Real nice.” If her face turned any redder she’d put make Big Mac himself look blue-furred by comparison. “I mean it’s big. Real big. Huge. Really impressive, BC — you should be proud! And you aren’t even hard. Are you? Are you getting hard?”

Finally, the non-stop stream of consciousness babbling ceased, and Cookie clammed up, her face scrunching into a cute, derpy expression before she groaned and slapped her hoof to her face, hanging her head.

“C-cookie.” Caisson finally finished a word. “S-sorry—”

“Don’t.” Cookie sighed, still hiding behind her hoof. “I told you I rambled when I got nervous. Here I am, acting like a tittering school-filly and sticking my hoof in my muzzle.” She groaned. “You must think I’m as silly as a foal.”

“No, not at all.”

“Ahem.” Cookie cleared her throat, letting out a little breath before holding her head back up again. “Let’s just go back a minute before I babbled on like a librarian with a parasprite infestation.”

“S-sure.” Caisson nodded letting out a sigh of relief.

There was such tension in the air, an inescapable energy that he had just never felt before — especially around his sister. Just this morning he had sat across from his little sister at their breakfast table, happily gulping down oats and only half-listening to her chirping about how excited she was to start at her new school. She was just his little sister after all.

But now…

It was like he was realizing for the first time that she was a filly. A mare even. The way she looked, the way she looked at him — even the way she smelled. There were two versions of Cookie in his mind — the one that he had taught to throw a buckball, the one that he had taught how to climb a tree: his cute little sister. The other version was the one he was just meeting now: a female that was not only interested in him — but also was dripping with sexiness.

Her beautiful face, her twinkling eyes, wild mane… lithe body and pert little athletic butt: it made his heart thump.

Caisson didn’t want to admit it to himself, but he kinda, sorta, maybe just a little bit… wanted to get a good look under her tail.

And that scared him — almost as much as it excited him.

“I’ll tighten your breech straps now.” Cookie said, affecting a professional demeanor. She glanced down at him, as if noticing for the first time “Ah, that’s a very nice penis BC.” The way she said it was as if she were grading a pumpkin at the county fair.

“Th-thanks?” He tried to hold back his laughter at her little act, almost made it too. But soon the chuckle escaped.

“Hey! Quit it!” Cookie growled at him, shaking a hoof menacingly. But shortly she was giggling too.

She rolled her eyes resignedly, before going back to work. Quickly, Cookie reached under him with her muzzle, getting her teeth close to the smaller buckles that rested along his inner-thigh.

Caisson stopped chuckling.

He could feel her breath along his lower belly now, warm puffs of air from her nostrils washing right over the base of his sheath, over his sack.

She’s certainly taking her time getting that strap settled — and did she really need to do it with her muzzle? She could have done it with her hoof, instead.

“Got it.” Cookie hummed. “You uh, smell really nice, BC. Just saying.” Her tail flicked out in a lazy whip.

“Th-thanks.” Caisson automatically replied. He wasn’t sure how a faceful of stallion-junk could smell nice though, it wasn’t like he had applied any deodorant down there, let alone one of mom’s perfumes or scented oils after his morning shower.

“Other side, now.” Cookie explained, her tail flicking again.

Caisson nodded, expecting her to remove her head from under his belly to walkaround him and lean in from the other side. He was caught off guard once again when instead the filly stepped further under his body, sliding her muzzle over toward the other thigh.

Of course, this meant that she was practically nuzzling the base of his stallionhood. The thick base where his organ met his belly now rested right across his little sister’s nose, draping the rest of his semi-flaccid stallionhood over her left ear and along her neck, the sensitive end of his pride bumping along her barrel.

“Mmmf!” Caisson moaned, unable to bite his lip shut in time. He had never imagined when he’d woken up that morning that he might end up laying pipe right across his little sister’s face.

He was intensely aware of every little movement as she fiddled with the buckle and strap, each shift of her head causing him to bounce and slide along the soft, short fur of her nose and face.

“Mfhthere.” A muffled confirmation of success came from between his legs.

But she didn’t pull right out from under him, instead turning her head underneath his junk as if the fact she was blinded by his stallionhood had caused her to get lost beneath him. She slid her nose more toward his rear end as she stepped even further underneath him, finally bringing his drooping mammoth of a dropped sausage right down the middle of her muzzle — the slowly stiffening tip of his stallionhood resting at the nape of her neck between her shoulderblades, like some obscene pink pool-noodle had been flopped onto the filly’s face, neck, and back.

She stepped forward, bringing her muzzle right underneath his balls. As she lifted up, her nose firmly embedded in the folds of leather-like skin, each of his pendulous orbs slid to one side of her muzzle.

And then he felt something, something wet.

He couldn’t tell if it was a lick, or perhaps the end of her wet nostrils flaring and snuffling, but it came with a heavy heave of Cookie’s barrel as she took in a deep inhale of his musty sack.

“Mmnghuck…” A strange moan came from beneath him, his sister’s cry drowned out in the dark flesh of his scrotum. He felt her tail brush up underneath him, ticking his ribcage as it lashed left and right wildly.

*Splat!*

A wet, pitter-spatter sound made his ears flick; somewhere under his body a half-cup of liquid had splashed against the ground.

That cinnamon scent became a fog. He could almost feel the humid heat of the pheromone-laden musk warming his body as the aerosol raced into his sinuses. His nostrils flared wide, heaving in air to gulp down the raw, sexual perfume... And everywhere the erotically infused oxygen raced through his blood stream he began to heat up, his huge heart pounded faster than when he’d run the quarter mile race at school, his muscles stiffened and throbbed, his hairs stood on end, his arteries and vessels expanded — as a wave of testosterone slid from his head to his hooves.

A wave that went right into his stallionhood.

A heavy pulse of red-hot stallion blood gushed into his groin, fattening the pink cylinder of flesh laying along his sister’s back with shocking speed. And each pulse was followed by another, the muscles of Caisson’s abdomen now letting a cascade of boiling, inflating blood gush into his massive stallionhood, lifting the huge beast of a penis as his heart pumped madly.

Inch after inch, his cock grew, sliding down his little sister’s spine, the bulging head bumping along each vertebra before the hydraulic pressure of his erection finally began to lift the mammoth thing off her body, slowly raising it with each thump of his heart up to his belly, as slowly as a drawbridge lifting to permit a ship to pass under it.

And each beat grew his erection too, transforming the already impressively large form of the once drooping slinky. His shaft fattened, thickening to a girthy, vascular log. His head expanded, growing wider and wider until finally, he felt the familiar touch of himself against a spot on his chest, just below his breastbone.

He had a boner.

“Ah, sorry about that.” Cookie’s voice floated up to him, as she began to extract herself from underneath him. Her tail swished left and right, its wild ends tickling his pink tip as her muzzle and head carefully extracted itself from underneath his body — leaving one last semi-nuzzle against his swollen base. “Got a little lost under th-”Cookie paused, taking in what Caisson assumed must have been a perfect side-on view of his shame.

“H-holy buck.” Cookie let out a breath, eyes wide in shock. “So that’s why they call you BPC.”

Oh crap. Caisson’s stomach dropped. She had heard about the incident.

Author's Note

Phew! Something seems to be going on with these two! Things are sure steaming up.

Guess we're gonna get to hear about 'the incident' now... what do you think it was?