Mutual Adoration

by Horndog

Rating: mature
Tags: Romance, Shining Armor, Sex, Twilight Sparkle, Porn, My Little Pony: Friendship is Magic, Fetish
Length: 7174

A young Twilight and Shining Armor's Nightmare Night costumes reveal just how much they admire each other.

As BBBFF and LSBFF, Twilight and Shining Armor share a sibling bond that defies convention, though their ideas for Nightmare Night costumes force the pair to realize just how deep their mutual adoration goes.

Their admiration isn't the only thing that goes deep that night.

Written for the Cloptober Wincest Contest!

Contains: Foalcon, Rimming, Deep Anal, Abdominal Bulges, Light Anal Gape and Inter-Sibling Mushiness.

Published 2024-10-31 09:20:00 UTC
Last updated 2024-10-31 09:20:00 UTC

The Feeling's Mutual

Adjusting the meticulously crafted paper mache horn cover, Twilight smiled at her reflection in the mirror. Gone was the young purple unicorn, and in her place stood a taller, lankier alabaster pony. It wasn’t perfect, but it was certainly the hardest she’d ever worked on a Nightmare Night costume, and the attention showed in the details. The hardest part by far had been covertly getting the measurements to ensure the details were perfect. She wanted to keep her costume a surprise to its likeness after all.

Fiddling with the long spiraling horn one last time to make sure it was at the perfect, slightly off-center angle it was supposed to be, she grinned in the mirror, adjusted her stance to match her appearance, and wobbled out of her bedroom door. Frowning at her limited mobility, she wondered if the stilt shoes she’d made to match the older pony’s height had been such a good idea, and those concerns only grew as she reached the top of the stairs. Biting her lip, she decided that there was nothing for it, and slowly worked her way down, one step at a time.

Triumphantly reaching the bottom, Twilight wobbled only slightly as she entered the living room, only to find fewer ponies than she expected.

Hearing a noise, a very lavender Shining Armor chuckled. “Finally. I thought you were going to miss Nightmare Night entirely. Mom and Dad already left to run Spider Toss, and my friends are gonna be here soon for trick-or-treating. What took you so long any-oh.”

The two siblings stared at each other, both getting an odd sense of displacement, as Twilight looked at herself as she’d probably look in a couple of years, and Shining Armor looked at himself as he looked now. “You dressed up as me?”

Reeling slightly from the accidental harmonization, Twilight was the first to recover. “You stole my Nightmare Night costume idea!”

Shining armor frowned, his purple eyes narrowing. “Nuh-uh! You stole mine! I’ve been working on this costume for months!”

“I’ve been working on mine for eleven months and thirty days! I had to account for my growth in this costume! I even had to lay off the extra sugary cereal in the morning cause my flanks were getting too fat to fit!” Twilight gestured with a foreleg to the sculpted foam inserts under the fake white fur that mimicked Shining’s coltish build, though her longer legs threw her off slightly and she ended up slapping her side instead.

“A whole year and you never bothered to practice walking in stilts?” Hopping off the couch, Shining approached his little sister, looking the costume over with a discerning pair of purple eyes.

“They were the last thing I made.” Appraising Shining’s costume in turn, Twilight smirked. “And I see you didn’t even try to maintain any kind of proportional accuracy. My flanks are not that wide.”

“Not yet maybe, but according to Mom, the moment she hit puberty her rump outgrew the rest of her for years, and it’s probably going to be the same for you.” Noting something, Shining smirked. “I see you forgot the scar on my shoulder.”

“I didn’t forget it. You only got it two weeks ago. I just didn’t have the time to rework the fur between then and now. Mom says it isn’t even going to be visible once your fur grows back anyway.” Wobbling only a little, her back legs nearly causing her to fall over for a moment before she righted herself, Twilight went on the offensive, circling her brother like a shark. “You didn’t even get my hair the right color. The blue is several shades too dark. It’s also much shorter than mine.”

“At least I got the eyes right.”

“They don’t make colored contacts for someone my age! I even looked into hexes that would temporarily change the color, but I couldn’t find any that didn’t have other undesirable effects.” Twilight pouted, stomping her wooden hoof.

“To be fair, I couldn’t find a mane growth potion that wasn’t horrendously expensive either. Though you could always end up changing your manestyle to look like this before you get this big.” Shining struck a silly pose, showing off his too-short mane and tail.

Twilight only rolled her eyes. “As if. I quite like my mane and tail this long, thank you very much. I read every book on style in the library before picking it. My mane perfectly accentuates the curve of my neck, and my tail is at the perfect length to remain light and airy while still offering mystique and allure by covering my-” Stopping dead in her tracks, Twilight could only stare.

Shining smirked. “I did a pretty good job didn’t I?” Wiggling his butt, he showed off the sculpted modeling clay pussy that seamlessly molded to his dyed ponut.

“You modeled my labia!? Why didn’t I think of that? I got the rest of the costume perfect, but I forgot your testicles and sheath! Though you still have your testicles uncovered. That’s not accurate anatomy at all.”

Shining coughed awkwardly. “Actually, I had that planned too.” Pointing to a lavender jock strap on the couch, he rubbed his neck. “I recolored my running strap from last season, but as I was waiting for you to come down, I realized I messed up and shrunk it while I was trying to dye it. It was getting pretty uncomfortable to wear.”

Snagging the offending article of clothing with her still developing telekinesis, Twilight looked over it. “No, it’s the same size. Your testicles have just gotten bigger.”

Shining raised an eyebrow. “They haven’t grown that much, have they? This thing was too loose on me last season. It should fit perfectly now.”

“You’re in the middle of puberty, Shiny. Though I must say your testicles have shown a higher growth rate than typical for colts your age.” Noticing something else, Twilight smirked. “And you missed a spot when dyeing your anus.”

“No, I didn’t!” Craning his neck around and flipping his tail up, he attempted to look at his own butt. “Did I?”

“You look so much less dignified than I would. Like a colt. It’s really breaking the illusion. Forget the missing spot, you’d never pass as me dancing like that.”

Pausing, Shining looked over to the younger unicorn with a deadpan expression. “Twily, I have seen you dance. You could have a stroke in the middle of the dance floor, and it would take till the music stopped for anypony to notice.”

Blushing beet red, Twilight bit her lower lip. “You just stand there and bob your head like a dork! And yes, you missed a spot! Right here.” Reaching out her stilted hoof, she poked his accurately padded ass a couple times before finding her mark and poking his ponut right on the inside edge of the ring.

Shining blinked, frowning in confusion. “Oh, there? What do you mean? I got it right.”

“No, you didn’t.” Twilight leaned in closer, inspecting the spot. “You’ve got a little pink spot that you missed.”

“Yeah, I worked really hard to get that right. It isn’t easy to dye your own tailhole dark purple in the mirror you know.” Shining gave an indignant huff, his back aching at just the thought of how long he’d spent hunched over in front of the bathroom mirror applying dye with a tiny makeup sponge on a stick.

Twilight’s eyes darted left and right as she thought, her face morphing into a frown. “You put that spot there on purpose? Why? I don’t have a spot on my anus.”

“Yes, you do.”

“No, I don’t!”

Rolling his eyes, Shining huffed. “Yeah-huh. Trust me.”

“My anus does not have any blemishes, I swear!” Twilight glared stubbornly at her wrong older brother.

“Here, c’mon and I’ll show you.” Bounding up the stairs to the bathroom, Shining waited impatiently for a moment. Poking his head back out into the hallway, he had another moment of whiplash as he saw himself at the bottom of the stairs looking up with a hopeless expression. “Twilight?”

Biting her bottom lip, accidentally smudging off some of the white lipstick she’d put on, Twilight shook her head. “I can’t go up the stairs in these stilts. I don’t want to fall.”

Looking around the bathroom, Shining spied his mother’s portable makeup case. Internally bemoaning the fact that he hadn’t even thought about its existence before spending two hours crouched on top of the bathroom sink, he grabbed it and headed back downstairs. “This will work.” Leading his younger sister to the couch, he helped her awkwardly roll onto it.

Laying on her back, her hind legs flopped to the sides, the weight of the solid wood stilts naturally pulling her legs into a pose that presented her small plot to the room. Grabbing the portable mirror in her own magic, she angled it so that she could see her protruding purple ring. “I was right, there’s nothing there!”

“No, Twi, you gotta relax. You can’t see it when you’re all clenched up like that.”

Huffing, Twilight’s indignant look slowly melted into horror as her ring relaxed, a small light pink spot emerging that matched the hint of pink just visible at the center of her anus. The analytical part of her mind noted that the splotch was simply a part of her skin that hadn’t received the pigmentation that made the rest of her ponut and by extension the rest of her exposed nethers a deep purple hue, but the rest of her mind was panicking. “No. Nonono! This can’t be! I have a blemish!”

“Relax, Twily. It’s not that bad. It’s not even very noticeable.”

“It’s very bad, Shiny! I have a blemish! No stallion is ever going to find me attractive, and I’ll die cold and alone in a little hermit shack in the mountains!” Twilight’s eyes had grown huge by now, her chest heaving as she hyperventilated.

Shining just looked nonplussed. “Because you have a tiny blemish on your butthole.”

“YES!” Baffled at Shining’s inability to grasp the gravity of the situation, Twilight just stared at him.

“I have never heard a single guy complaining about a blemish before.” Shining paused as he had a thought. “Actually, where did you read about this?”

Twilight blinked, biting her lower lip in thought. “Mares Monthly, issue 1494.”

“And what was the article about?” Shining smirked, already knowing the answer.

“It… was an ad. For a beauty cream that’s supposed to remove blemishes.” Twilight frowned. “But that doesn’t mean it isn’t true!”

Shining couldn’t help but roll his eyes. “Even if it was, I hope you don’t date a stallion so shallow that he cares about something as small as this. Your inherent neuroticism is a much larger roadblock to your future relationships.”

“HEY!” Twilight swatted her older brother’s shoulder, the wooden stilt only mostly blocked by his costume’s added padding.

“I’m kidding, I’m kidding!” Rubbing his shoulder with a hoof, Shining leaned in close. “But seriously, nopony is gonna notice your little spot. Even you didn’t notice it until now.”

Twilight shook her head. “You noticed it! And when I do go looking for a coltfriend, they’re bound to notice it when they’re appraising my sexual attractiveness in preparation for mating!”

Attempting to head of a second bout of panic, Shining scooted closer. “And they’ll find it just as cute and endearing as I do.” Redirecting Twilight’s gaze to the mirror, Shining smiled down at her butt. “Look, doesn’t it look like a heart?”

Looking in the mirror, Twilight realized that once again, she’d tensed up, the blemish hidden in her puckered folds. Taking a deep breath, she relaxed, slowly revealing the offending mark. It did kind of look like a heart. A slightly lopsided one, but she could see it. “That doesn’t change the fact that potential future suiters could find it unattractive.” Her moment of calm failing, Twilight once again began hyperventilating.

Thinking fast, Shining leaned down and planted a kiss right on her tightening pucker.

“Sh-Shiny? You… you kissed my butt.” Panic forgotten, Twilight could only stare at her older brother. Who just happened to look like her at the moment. With her brain rebooting, something about the visual oddity of looking at herself staring with an enamored look on her face at her own butt reshuffled some internal cataloging and suddenly the blemish didn’t seem so bad.

“Well, you know, when you’ve got a boo-boo, you kiss it to make it feel better, right?” Shining grinned awkwardly, scratching the back of his neck because the costume was itchy, and no other reason.

“My anus doesn’t hurt, Shiny.” Twilight was still a little lost, but any opportunity to poke fun at her older brother was taken, even if only by reflex.

“It was hurting you, though. Even if only emotionally. And, well, I did kind of want to kiss it. Your ponut is very attractive, Twily. I want you to know that.” To prove his point, Shining went in for another kiss.

Giggling, Twilight noticed something out of the corner of her eye. “Your penis is out of its sheath.”

Resting the natural urge to hide it, Shining just grinned. “See? That shows that I’m telling the truth.”

Grinning back, Twilight shook her head. “Nuh-uh. You’re a colt in the middle of puberty. You got an erection looking at the curves of a book the other day.”

“For your information, I was thinking about how I was going to model your pussy out of clay, so by proxy I was thinking about your butt even then.”

“And when you were folding laundry yesterday?”

Shining had the decency to look embarrassed. “Well, the bedsheet kinda fell in a certain way, and it looked sorta like the wrinkles on your tailhole…”

Twilight took a moment to process that information. “So, you’re telling me you just think about my butt all the time? Do you look at a picture of a heart and think about my anus then too?”

Shining only cleared his throat, looking at the wall.

“Wow. Okay. You really do like my butt. That’s… huh.” Looking at the mirror again, Twilight took a moment to inspect her little hole. “Is it really that special?”

Shining coughed. “Well, as far as butts go, yours is nice and tight, and very well shaped for a filly your age, but mostly it’s that it belongs to you. There’s…” Biting his lip, the colt thought about what he was about to say. “There’s a reason I wanted to dress up as you for Nightmare Night. Fillies and colts everywhere dress up as either silly monsters or other scary things, or as characters they look up to. Supermare, Batmare, firefighters, royal guards. I wanted to dress up as you, cause I look up to you. You’ve barely gotten your magic in yet you’re already way better at it than I am. I’m no slouch at school but I still have to turn to you for the harder questions, and you’re my younger sister! And, also, I wanted to look like you cause I like looking at you. You’re already attractive, and as soon as puberty hits, you’re going to have colts knocking at your door from miles around.” Shining chuckled. “If you can pull your nose out of the books for long enough to answer that is. What I’m trying to say is…”

Twilight smiled up at her older brother, seeing the older brother she loved even through the fancy makeup and padded purple suit. “I know. I get it. I think. I guess I dressed up like you because I wanted to be you for a night. To be the big brave older brother. My BBBFF. I wanted to be the one to keep a watchful eye for the ponies around me. I wanted to be the one to secretly split the candy stache forty-sixty in the middle of the night and then claim that my pile was smaller cause I ate a bunch of them during the night.”

“You knew about that?” Shining raised an eyebrow, surprised.

“Duh. I counted and indexed my candy as I got it throughout the night. A twenty percent increase in candy was very noticeable.” Twilight giggled.

“Of course you did.”

The two laughed together for a moment before the clock chimed, reminding them that it was Nightmare Night and Twilight was laying butt up on the couch with Shining standing over her, his cock throbbing.

Shining looked down at his younger sister, and even through the admittedly very impressive costume, all he could see was the filly he loved. Looking into her curious eyes as she eyed his bobbing length, Shining was overcome with a sudden fire in his loins, an urge that his teenage mind would not deny. He just had to figure out how to steer the current situation in just the right way to fulfill it.

Looking down her costume again, proof of her own admiration of him, his eyes were once again drawn to her small pucker. “Y’know, there’s another issue with your costume.”

Looking up from his cock, Twilight raised an eyebrow. “What other flaws have you found in my hard work, oh brother of mine.”

“Oh brother of…” Shining stared, distracted by the sudden shift in Twilight’s vocabulary. “Has mom been reading you Shake Spear before bed?”

For her part, Twilight only giggled. “Mayhaps.”

“My little sister is gonna grow up to be such a nerd.” Shaking his head to clear it, he regathered his thoughts. “Anyway, as I was trying to say, your costume has a flaw.” Extending a hoof to boop it, Shining proclaimed, “Your tailhole is far too cute and tight to ever pass off as mine.”

Twilight thought for a moment, peering down her own dyed white belly as if to catch a glimpse of the protruding ring. “Yours is much looser than mine, isn’t it. Is it because you’ve been sitting on your empty shampoo bottle again?”

Shining’s blush burned through the lavender dye on his own fur as he fumed in embarrassment. “That was one time!” More faintly, he muttered, “Though that did probably permanently stretch me out back there once I got it in.”

The younger sibling’s natural instinctive ability to rub salt in the wounds of embarrassment kicked in, and Twilight’s grin only grew. “Or was it Mom’s hairbrush? Or maybe it was that crabapple. The toothbrush handle? Or was it the-”

“Alright, enough! I get it! I get it. I’ve stuck a lot of things up my butt during my years. It’s not my fault it feels so good!” Wrapped up in his indignation, Shining missed the thoughtful expression on Twilight’s face. “Anyway, what I was trying to get at was that I was going to offer to be the helpful brother and help you with your costume, but now I don’t even know if I want to anymore.”

“And how exactly were you planning on helping me make my costume more accurate?” Twilight asked, already having an idea in her mind of what he was planning.

Shining blinked, suddenly unsure of his grand master plan. “Well, uh, you see, um… With how your tailhole is too small, you know, for the costume, not in general, your tailhole is actually really nice, but uh, I was thinking I could, uh, y’know, to help, uh, with your costume, maybe I could help you, uh, stretch it out?“

Looking up at the trainwreck that was her currently lavender older brother, Twilight gave a lidded expression. “You just want to stick your penis in my butthole.”

Caught red hooved, Shining sighed. “Well… yes?”

Rolling her eyes, Twilight snorted. “You could have just asked, dumb dumb.”

Shining blinked, caught entirely off guard by the comment, having expected disownment followed by banishment. “Wait, what?”

“With how you’re always going on about how good it feels every time you get caught or called out about sticking things up your butt, I’ve gotten pretty curious about it, but I’ve never been brave enough to stick something up there myself.” Looking up with big innocent eyes, Twilight asked, “Could you help me?”

Completely thrown off, having never thought he’d get this far, Shining only stared for a moment in a stupor. Finally blinking, he was caught out again for a moment by her costume as his brain restarted. “Twily, I… Yeah. I mean, yes. I’ll help. Anything for you.”

Twilight considered ribbing him a bit more but decided to spare him. “So, how do we start? What do we do first?”

“Well, uh, what I’ve discovered is that lubrication is super important. Like, rule number one. So, uh, if you don’t mind, I learned a spell out of the back of one of Dad’s old magazines that I’ve found works pretty good, though I will warn you it feels weird.” Lighting up his horn, Shining stuck out his tongue as he concentrated, the simple spell taxing on his adolescent horn.

Twilight’s eyes widened as a sudden warmth started at her anus and raced inwards, making her shudder as it felt like it went around way too many loops and bends before she suddenly felt hungry. “Whoa. Did that spell go through my entire gastro-intestinal tract?”

Shining shrugged. “Maybe. The magazine just said ‘For clean, safe and well lubricated fun’ or something. I didn’t pay much attention past that. I’m not an adorable little bibliophile like you.”

Sticking her tongue out at Shining, Twilight was wholly unprepared for him to stick his own tongue out in return before lapping it across her butthole in one big swipe. “Whoa! That felt funny.”

“Huh. The article wasn’t lying. It does taste like strawberry.” Going in for another lick or twelve, Shining was treated to a series of cute noises as Twilight got used to the sensation.

Twilight, for her part, was holding on to the couch as best she could with stilts as her older brother lapped and sucked at her butthole like an enthusiastic dog. The sensation had felt akin to tickling at first, but as it went on it felt more and more like it was building a different kind of heat between her cheeks.

Stopping for a moment, Shining took the opportunity to change his approach.

Twilight’s breath hitched as the tongue that had been lapping at the outside of her tight ring began attempting to spear through the center of it instead. “Shiny! What are you doing?”

Pausing, Shining retracted his tongue. “Well, with how tight you are, there’s no way my penis is going to fit inside you unless you loosen up and relax, and a few of the adult books I snuck out of the library mention the stallion using his tongue to do that.”

"So, you’re going to stick your tongue up my butt?” Twilight frowned, having a hard time wrapping her head around the concept. She knew about anal intercourse from the encyclopedia, but that only mentioned inserting a penis, not a tongue.

“Well, yeah? Supposedly I could use my horn instead, but that’s supposed to be for more experienced ponies.”

Wrinkling her nose in concentrated thought, Twilight muttered to herself, “You can stick your horn up there?”

“You can stick anything you want up there as long as it fits and isn’t dangerous, Twily.” Booping her adorable snoot with a hoof, Shining smiled.

Shaking her head, Twilight bit her lip. “Well, it was starting to feel interesting... I suppose you can continue.”

Without waiting another moment, Shining dove back in, trying to wriggle the tip of his tongue into her impossibly small ponut. After a few moments of effort, he could feel her sphincter relaxing just enough to let him in.

Twilight let out a squeak, her eyes going wide as Shining’s tongue, now given the opportunity, slipped deep into her rectum. All at once the vaguely ticklish sensation changed to something much different. Much better. As his tongue explored inside her, it kept brushing against a spot that made the odd heat burn bright for just a moment. Letting out a gasp, her entire core tensed for a moment, leaving her feeling tingly.

Shining’s eyes lit up in delight as he watched his little sister wink for the first time, her adorable little clit peeping out at him for just a moment. Spurred on by the sight, he doubled down, working his tongue deep enough to fill her entire smaller rectum. Swirling it around her tight cavity, he worked on the area that the magazines said was supposed to be more sensitive.

Shining’s vague recollection of a magazine he’d read in a corner store once proved true, Twilight’s breath hitching as her older brother doubled down on that hot spot inside her butt. She couldn’t believe it; he’d been entirely right. While her brain was still attempting to categorize the feeling she was feeling, the consensus was that it was good. Very good. Sort of a cross between a tickle and the feeling of a good massage, but whatever it was it was contributing to that delicious warmth in her loins that she was quite enjoying.

Twilight attempted to communicate that as eloquently as possible, but the only noise she managed was a squeaky moan. It was good enough for Shining though, who burrowed even deeper into her rectum, his lips wrapping around her clenching ring and applying a gentle suction.

Having explored Twilight’s rear entrance as thoroughly as possible, her ring having loosened considerably under the ministrations, Shining pulled his tongue out of her butt with a pop. Looking at the fruits of his labor, he smiled. From the lightly gaped, twitching ring of her sister’s butthole, her little heart shaped mark on full display to the adorable expression of bliss on her face, the only thing marring the experience was the fact that other than the lack of a package, it looked like himself on the couch.

For a fleeting moment, the thought that crossed Shining’s mind was that he looked hot as a girl. Shaking his head vigorously to dissuade further thoughts, he asked, “So, how’re you enjoying your first time, Twi?”

Taking a moment to collect herself, Twilight looked up at the spitting image of her older self. “It’s… different than I expected. It’s good though. I think. More intense. I’m sweating a lot, it feels like there’s a burning heat in my core, though that might just be from the padding.” Looking down her body at Shining’s rigid length, she bit her lip. “Are you ready to put your penis inside me yet?”

Holding himself back from doing just that, Shining looked down at his little sister. “The real question is, are you ready? It’s your butt on the line, not mine. Literally.”

Biting her lip again, Twilight thought for a moment. “Yeah, I think I’m ready to at least try. At least after you’re done with your terrible puns, ya dork.”

“Excuse me, I’ll have you know that now is the perfect time for puns. I’m trying to help you loosen up after all.” Laughing as she clobbered him with a stilt, Shining looked down at Twilight. “Though if you’re ready, let’s give this a shot.”

Putting his front hooves on the couch to the sides of Twilight’s head, Shining attempted to line his stiff member up with his target. Biting his lip in concentration, he missed a few times, poking her butt cheeks and mashing against her dock. Adjusting his hips just slightly, he found his mark, pressing against her tiny ponut. “Ready?”

Twilight nodded, taking a deep breath as she tried to relax. “Yes. Put your penis in me.”

The innocent determination in her voice resounded in Shining’s ears, shaping his tastes and forming the foundation of a preference that would last his whole life. Fueled by this newfound need, he pressed forward more firmly than he would have dared otherwise, and after a moment of straining, his flared head popped through Twilight’s taut sphincter.

Twilight’s eyes went wide. After a brief sensation that felt like when she overextended her jaw while yawning except in her butt, she now felt very very full. And stretched. She could feel with incredible clarity the sensation of her sphincter muscles clenching, almost pulsing against the invading object.

Shining’s eyes were also wide, the feeling of Twilight’s impossibly tight pucker wrapped around his tip leaving him stunned. He could feel her rapid heartbeat in the walls of her rectum, and the rhythmic clenching of her ponut wrapped just behind his head. Blinking, he realized he’d stopped breathing some time ago. Taking a couple of deep breaths, he looked down into his sister’s eyes. “Are you okay? How is it?”

“Wow.” Struggling to think of something more intelligent to say, Twilight eventually came up with, “Is this what anal intercourse is then? I like it.”

“Well, kinda.” Trying to think while his tip was getting squeezed by his sister’s tight ponut was hard, but Shining did his best. “This is just the start of it. I’m supposed to put my penis all the way inside your tailhole and then pull it out again over and over.”

“All the way inside…?” Twilight’s eyes unfocused as the thought permeated her brain. The description for anal intercourse had been brief and lacking in detail, only saying that it was the act of inserting a stallion’s penis inside the anus of another for the purposes of pleasure, and Shining had already done that. Though she supposed that he hadn’t put it all the way in yet. She didn’t know if it would fit. His penis wasn’t nearly as big as Dad’s yet, but it had been growing steadily since he entered puberty.

“Yeah. Or at least that’s what the pictures showed. And then you sorta just go in and out in a rhythm with a plapping noise. It’s the friction that’s supposed to feel really good.”

Wiggling her butt slightly, Twilight focused on the feeling of what Shining had already put in her and realized that it had popped in without too much trouble. “You’ll stop if I tell you to, right?”

Shining nodded enthusiastically. “Of course, Twilight. You’re my sister, I don’t want to hurt you.”

There was only one way to find out if it would fit. “Alright. Go slowly though. You feel really big in my anus.”

Steadying himself, trying not to let the compliment go to his head, Shining began working his length into her rear, slowly but surely stretching her virgin tunnel. Twilight’s breath hitched again, her pupils dilating as his flare dragged across that spot inside of her that felt so strongly. She tried to find a better way to word it in her head, but the pleasure emanating from her bottom half was overwhelming enough that she was having trouble even keeping her eyes focused on Shining’s above her.

It didn’t take long for Shining’s length to fill her small rectum front to back. His medial ring was nearly touching her anal ring when he felt the sudden change in texture and tightness at his tip. Looking down at Twilight’s absolutely enamored expression, her unblinking eyes gazing up into his with a love and passion that exceeded her small frame, he realized he must have looked the same way to her. “Are you doing alright? Do you want me to go deeper?”

Taking a shuddering breath, Twilight fought to remember her anatomy books, gauging the diagram against what she was feeling inside. The foreign feelings in her butt were hard to place, but she was pretty sure she knew what was going on. “You’re at the entrance to my colon. The… sigmoid colon? Can a penis fit in the colon?”

Shining bit his lip. “I don’t know. None of the stuff I’ve read mentions it. Maybe?”

Taking stock of how much of Shining’s member was inside her already and how much was left to go, measured against her recollection of the anatomical diagrams she’d seen, Twilight reasoned that his tip would stop just short of the bend into her transverse colon if he fit his entire length inside of her. Gauging by the length of their Dad’s penis and the relative size of their Mom, if they ever performed anal intercourse the tip of his penis would just extend past the end of her rectum. “I think it should. Just go slow and I’ll tell you to stop if it gets to be too much.”

“Of course, Twily.” Even more slowly than before, which Shining was partially glad for considering that he was already feeling pretty close to orgasm, he pressed on. Before he’d even really had a chance to go deeper, his medial ring pressed against her straining pucker. Larger than his flare had been, her sphincter put up some resistance, though with how much more relaxed her puckered entrance had become and the additional lubrication leaking from her untouched fillyhood, it didn’t take much to overcome, and with a breathy grunt from Twilight, her ponut slipped over the bump.

Closing her eyes for a moment to get used to the increasingly odd feeling of her sigmoid bend being straightened, Twilight let out a squeaky moan at the twin feeling of the walls of her anal cavity being stretched out even more deeply and Shining’s medial ring scraping across her g-spot as he sheathed the rest of his member in her butt.

“Whoa, Twily…”

Opening her eyes again, Twilight looked up to see that Shining’s eyes had shifted to her stomach. Looking down at her whitened fur, her own eyes widened as she saw what he had. Her normally flat stomach had a distinct bulge just to the side of her belly button, betraying just how deep her brother’s tip was inside of her. The both of them only stared at it for a moment before Twilight broke the silence. “Wow… You’re so deep inside of me, Shiny. I can feel it too. There’s so much of you inside of me. It’s… incredible.”

“You feel incredible too, Twily. You really are amazing. I love you.”

“I love you too, Shiny.” Pressing her butt against Shining’s crotch in an attempt to get his member even a little bit deeper into her butt, Twilight looked up at him with a hunger in her eyes. Her body felt like it was on fire from how intense the warm feelings radiating from her core were, and she wanted more. “What are we supposed to do now? Something about friction?”

“Yeah, I just need to pull out and then put it back in again, but faster this time now that we know it fits.” Pulling his hips back, the only thing Shiny managed to do was drag Twilight along with him, her walls gripping too tightly around his shaft to allow an easy exit. Pushing her back onto the couch, he repositioned his forelegs under her armpits to give her something to brace against.

Trying again, he was met with success, Twilight’s eyes crossing as her tight ring was tugged on by the force and her walls stimulated so deliciously as Shining’s medial ring and flare pulled out with a sucking pop despite her body’s best attempts to keep them in. Her heart panged as she was left achingly empty, her muscled walls clenching around nothing in the absence of her brother’s penis.

The absence was short lived, however; Shining just as eager to fill Twilight back up again as she was to be filled. Having been stretched out already, her loosened ring gladly accepted his member back inside, the entire length of his colthood slipping into its proper place in one smooth thrust.

Staying hilted for just a moment, the pair savoring their closeness, Shining pulled out again with a pop, Twilight’s insides letting him go even more reluctantly than last time. There was no hesitation this time as he drove himself back in to the hilt, brother and sister moaning in tandem as they stared deep into each other’s eyes.

It couldn’t last forever though, especially with Shining’s pubescent stamina. “I’m close.”

Looking up at her big brother, completely enamored, Twilight smiled. “I love how close you are. It feels like you’re surrounding me, inside and out.”

Shaking his head, Shining halted his thrusts, staying fully hilted. “No, I mean to climax. Orgasm. I’m about to shoot my seed. Do you want me to do it inside or out?”

Blinking, Twilight considered for the first time that there might be a climax to the building wellspring of pleasure in her core, even though it felt like it would just keep building forever. Turning her thoughts to the question, she scrunched her eyebrows in confusion. “Does it matter? You can’t get my butt pregnant. I’m not even ovulating yet anyway.”

Shining blinked. “Oh. Yeah. It’s just something they ask in the books, but I guess none of the mares were your age. Inside then?”

Wishing that Shining could just stay inside her forever, Twilight simply nodded cutely. Her wish was almost immediately broken as Shining pulled out again, but the sensation of his growing flare dragging along her insides as it exited only to plunge back in again was plenty to fuel the raging fire in her core. Two thrusts later and she figured out why it was called climax.

The pleasure that had been building steadily suddenly skyrocketed, her whole body tensing as she came, her legs wrapping around Shining’s hips to hold him as deep inside her body as she could.

Shining wouldn’t have been able to pull out even if she wasn’t holding him, her entire tunnel going from tight to nearly crushing as her internal muscles rippled along his length from base to tip, as if trying to milk the seed from his balls. It worked, Shining gritting his teeth as the most intense orgasm of his life washed over him, his testes visibly pulling up in his sack as they worked to unload every drop of his watery seed as deep into his sister as possible.

Even as overcome with the sensations as she was, Twilight’s hypersensitive tunnel could feel Shining’s flare spread the walls of her colon just a bit wider before clenching regularly, and her pupils dilated as she could feel an additional bit of warmth pooling just a bit deeper inside of her gut. It felt like every neuron in her brain fired simultaneously, her every sense in perfect clarity as her mind committed this exact moment to memory, forming the cornerstone of her sexuality in a single instant.

The moment was over all too soon, leaving the two siblings panting as Shining’s colthood shrank, falling out of Twilight’s ass with a much softer pop. Taking a step back, Shining could only stare.

If the goal was to stretch her out a bit, they’d more than accomplished it. Twilight’s once cute, tight and virginal ponut was now a sloppy wet ring, the dark purple band twitching as if trying to hide the light pink of her stretched out rectum but it just couldn’t muster the strength to. “Woah. Twilight, your tailhole…” Spotting the heart shaped mark that had started all this, he was transfixed. “It’s amazing. You’re so beautiful, Twily.”

Laying back on the couch, taking ragged breaths as she already wondered when they could do this again, Twilight smiled. “I love you so much, Shiny. Thank you.”

“I love you too, Twily.” The clock’s chime rang out, causing both to jump. “Whoa! How did it get so late? We really are going to miss Nightmare Night!”

Ignoring her brother’s scrambling as he worked to get his costume back in order, Twilight’s goofy grin didn’t fade. “I’ve already had the best Nightmare Night I could ever ask for.” Eventually roused from her stupor by Shining pulling her up and onto her hooves, the stilts having fallen off at some point during their lovemaking, she looked up at her big brother with open adoration in her eyes.

“My friends were supposed to have been here by now! Maybe they knocked and we missed it cause we were too busy? It doesn’t matter, we need to get going or ponies are going to get suspicious.”

Twilight simply shrugged, following her BBBFF out the door to join the throngs of ponies celebrating.

The older of the two Twilights smiled and waved as she caught sight of her two children entering the square. Noticing that ‘Shining Armor’ looked a little short, she frowned. She’d helped with the stilts, but apparently, they hadn’t worked. Oh well. Her daughter looked happy enough. Almost too happy. Nearly glowing. Had she gotten into the candy early? Shining looked slightly ragged, probably from trying to keep up with a sugar-high Twi. The pair hadn’t caught sight of her yet, but she was content to watch from a distance as her foals wandered around the attractions.

Admiring her handiwork, having helped both of her foals with what she thought was the cutest costume idea ever, she noted with satisfaction that from a distance, you’d have never known the two had traded identities if it weren’t for the height difference. And the dye that was streaking off Shining’s hind legs. Frowning, she noted that the dye was actually coming off both siblings’ back legs.

Telling her husband to hold down the fort for a moment, Twilight Velvet approached her children until the sight of her daughter turning to talk to her older brother stopped her dead in her tracks. Most of the white dye had been rubbed off Twilight Sparkle’s rear and it was easy to see how it’d happened, a trickle of white that wasn’t dye seeping from her still lightly gaped anus.

The crude jokes about pegging that had been tossed around by a gaggle of unruly teens that she thought she had recognized as Shining’s friends earlier in the night suddenly made sense. Her foals were late because they’d been fucking each other, and apparently in view of the living room window.

Twilight Velvet had thought she’d still had time to talk to Shining about his obsession before he acted on it, but it was obviously too late for that. And from the looks Twilight was giving her older brother, it was also pretty obvious she’d have to have a talk with her too.

What was also painfully clear was that the two couldn’t be left alone together anymore either. Turning around and briskly walking back to her husband to have a discussion with him about all of it, Twilight Velvet decided that they’d need to have a babysitter from now on. She’d seen a flyer at work advertising the services of a young pink mare. Surely her presence would work to stop her foals from having sex again...

Author's Note

Actually managed to finish one of these in time!
Hope you guys enjoyed the mush! :twilightblush: