“This is nice,” Twilight commented as she relaxed further into the warm embrace of the pony behind her. Splotches of mid-afternoon sunlight danced along her plumage and over her coat, filtered by the swaying leaves of the impressively-sized apple tree canopy above. Audible only to her, a soft “Mhh-hmm” was Shining Armor’s reply. His muzzle hummed against the back of her left ear, tickling it and encouraging a few reactionary flicks before he captured the appendage in his lips, suckling lovingly as he cradled his sister in his hooves, his back pressed into the rough bark of the tree.
Twilight sighed in contentment.
“I told ya this place was perfect,” Applejack said. “One o’ the best-kept secrets of the Acres. Mac an’ I are the only ones who ever come here, whenever we need some... time alone.” She chuckled, leaning over to give Big Macintosh a quick peck on the lips. “It’s kinda strange havin’ company for once... but it’s kinda nice, too. Makes it feel less like we’re hidin’ something and more like... just some ordinary picnic with friends.” She pushed up her Stetson thoughtfully. “’Cept it’s really more like two pairs o’ special someponies, I guess.”
“A double-date,” Twilight clarified matter-of-factly. “I said before that’s what it was.”
“I dunno. A ‘date’ always makes me think of gettin’ all gussied-up and goin’ to fancy restaurants or movies or somesuch.”
The alicorn shook her head. “No. A date is any scheduled social engagement, usually between romantic partners. A picnic definitely counts. I’ve read up on the subject.” She grinned as she levitated some small remnant of dessert from the checkerboard-patterned blanket in front of her and popped it casually into her mouth. “Trust me, this is a double-date.”
The grin was clearly infectious. “I s’pose. Well, whaddaya know, Mac? Turns out we’ve been datin’ for years!” The orange earth pony laughed.
Her stallion pursed his lips in brief consideration. “Eeyup,” he concluded.
A short-lived silence settled in over the happy quartet.
Big Macintosh nuzzled his sister.
Shining Armor kissed his.
Finally, he spoke up. “This really is a great spot. Thank you, Applejack. It means a lot to me and Twilight to be able to be out with some other ponies who understand the kind of relationship we have.”
“Aww, shucks, think nothin’ of it. I know how hard it can be, keeping somethin’ like this all to yourself for so long. I just wish Twi here woulda said somethin’ sooner.”
“I could say the same for you!” the purple mare countered. “I always suspected you and Big MacIntosh had something going on, but I didn’t want to say anything because... well, you know...” Her hooves were suddenly rubbing in nervous circles. “It’s sort of a stereotype...”
Another snicker from Applejack. “You mean country folk, right? We’re all just a bunch of inbred yokels?”
Twilight gasped. “No! I... I didn’t mean it like that!”
“Relax, sugarcube. I know whatcha meant.” The earth pony threw her friend a calming smile. “But I also know the opinions some folk have. That’s sorta why Mac an’ I have been extra careful to hide our special time together.” Her brows furrowed. “How didja suspect us, anyway?”
The alicorn shrugged. “I’m not sure. Maybe it’s something about the way you’d look at each other. It reminded me a little of the way Shining Armor and I did. I don’t know, really. It wasn’t logical. Just something I could feel, but I could never put my hoof on it, so I ignored it.” A look of sudden worry clouded her face. “Did... did you ever suspect anything? About us, I mean?”
“Well...” Applejack’s countenance scrunched up in thought. “For a while, I didn’t even know you had a brother, so I can’t say I was hikin’ down that trail, but...”
“...but...?”
The earth pony smiled with half-lidded eyes. “Just some friendly advice for ya, Twi: Try not to act like a jealous girlfriend when you find out your brother’s gettin’ hitched.”
The purple mare’s cheeks flushed a vibrant pink. “It was that obvious, huh?”
“You were actin’ a might possessive.” Seeing the unicorn’s increasingly distressed reaction, Applejack quickly amended, “Ah, don’t worry about it. I don’t think anypony else caught on; I wasn’t even sure myself. I’m mostly just teasin’ ya.”
Twilight calmed somewhat, her rosy face returning to a more familiar lavender hue.
“Speakin’ of, how is the princess?”
“Cadance is doing great,” Shining Armor replied. “She’s really gotten the Crystal Empire running smoothly, and everypony just loves her. With the Equestria Games coming up, the whole Empire is rallying behind her. It’s really amazing to watch.” The stallion stared at some image in his mind’s eye – likely his wife’s – and smiled. “She says the trick is not to try to do everything yourself, but to find the right pony for every job and let them handle it. That’s probably why she doesn’t let me do anything important.”
Applejack briefly hesitated at the self-deprecating joke, but seeing both unicorn siblings chortle between each other convinced her that it was alright to join in.
“I still can’t believe Cadance is alright with you two canoodlin’ around with each other like this.”
“She’s a very open-minded pony,” Shining Armor explained. “We all came to an arrangement pretty quickly. Plus, she sort of has a... fetish... for forbidden love. She’s actually been encouraging me to find ways to spend more time with Twilight.”
The earth pony leaned further back against her own brother as she regarded the royal siblings with a wry smile. “Well, I’ll give ya this: You two sure do look cute together. Don’tcha think so, Big Mac?”
“Eeyup.”
Twilight blushed once again, this time joined by her brother, as their stares wandered shyly away into the surrounding grass. Applejack and Big MacIntosh laughed.
With time – and much indignant scowling – the other pair did, too, the mirth building until it reached a joyous crescendo, as everypony basked in the glow of the moment, quite possibly having already forgotten the joke which had been its catalyst.
Ultimately, the spent ponies returned to the blissful post-meal silence of before, though over the course of the next few minutes, Applejack’s eyes kept returning to the pair of incestuous lovers.
“Something on your mind, Applejack?” Shining Armor asked.
The mare casually waved off the suggestion. “Nah, nothin’ worth mentionin’.”
“I'd like to hear it anyway,” Twilight voiced, capturing the others’ attention.
Applejack's sight veered away. “It's really nothin’,” she lied – badly – mumbling the denial from beneath her hat’s brim. Solace was not to be had in the face of Big MacIntosh, who locked eyes with her in a curious gaze; inquisitive rather than sheltering.
“You were never a very good liar, Applejack,” Twilight teased gently. “It's nothing bad, is it?”
“No, it's...” Fresh blood shone through the farmpony's cheeks as her hooves played with the tie of her blonde ponytail. She sighed, though on this occasion it was a sigh of palpable anxiousness. “Y– You'll just think I’m bein’ a silly pony...”
The other mare gingerly giggled. “I doubt that. I often have strange ideas; I'm sure everypony does. Unorthodox thoughts, even ones that seem to make no sense, are often a symptom of creativity... even intelligence.”
A snort. “Well, in that case Pinkie Pie must be a bona fide genius.”
Another round of laughter served only to delay the inevitable, as Twilight refused to let the issue go. “Come on, Applejack. Let’s hear it!”
At this point, even the stallions were rapt with curiosity and making encouraging gestures.
“I was just thinkin’... not serious-like, mind you... that Big Mac and I are brother an’ sister, and so are you two, and it’s kinda weird, us bein’ two pairs o’ kissin’ kin...” Applejack’s ears were down flat. Her hat had been removed, and she clutched it to her chest like a little filly would a protective teddy bear. “...and how it’d be even weirder – but more normal at the same time – if we... switched.”
Although everypony’s eyes momentarily expanded, the shock quickly gave way to a calm, quiet, and slightly embarrassed contemplation.
Twilight was the first to speak. “You mean, like... if we swapped sexual partners?”
With one hoof, the orange mare dug into the back of her mane; with the other, she fanned away the heat continuing to build on her face. “Yeah… Like I said, it was just a silly idea. Heh. Don’t rightly know why my mind even went there. Not like it’s ever gonna happen.” She chuckled, hugged her brother for comfort, and was hugged in return.
“Why not?”
Everything stopped. The wind. The grass. The birdsongs and the leaves on the trees. Everything held in place as all attention turned to the alicorn who had spoken those words.
They were magical words, imbued with power few could truly appreciate; words that had, countless times since past immemorial, across realms, generations, and ideologies, opened up the world to hitherto-unknown possibilities.
Here, on a warm and sunny afternoon on a secluded, breezy hilltop beneath a ripe apple tree in the rolling farmlands outside a tiny Equestrian town, those two words would not disappoint.
“I… I mean… speaking hypothetically, there’d be nothing morally wrong with it,” Twilight clarified, her own face beginning to glow near crimson despite her best efforts to hide it under the fringe of her mane. “If– if everypony involved is consenting and it’s something we all want– we would all want to do, then… then there wouldn’t be anything stopping us, right? Hypothetically.” She coughed and made a poor effort to look nonchalant.
“Hypothetically,” Applejack echoed, the heated embarrassment on her face not so much fading away, as being forced to share space with a growing expression of wide-eyed marvel. She shot Big MacIntosh an inscrutable look, before turning back. “Twilight… have ya ever… wondered?”
The alicorn bit her lip, holding onto the answer for a few painfully awkward seconds before saying, “Yes.” She refused eye contact.
Shining Armor at last came to his sister’s aid, clearly fighting down his own inhibitions to do so. “Most ponies fantasize like that; imagine themselves in sexual situations with ponies they know. It’s perfectly natural and healthy; Cadance always said so, and she’s the expert on this sort of thing.”
The earth pony mare nodded her agreement. “Yeah, I reckon…”
Twilight cleared her throat. “I agree. And we shouldn’t be embarrassed talking about it. I mean, none of us here are prudes – certain stereotypes about librarians notwithstanding – and we already know more about each other’s sex lives than anypony else. We’re all friends, we’re all mature, we can trust each other, so nopony should feel uncomfortable discussing a few risqué fantasies… right?” The last word came out halfway between a question and a plea.
“Yeah,” Applejack asserted, straightening her posture.
“Sure,” Shining Armor said with a confident tone.
“Eeyup,” Big MacIntosh confirmed their unanimity.
A relieved exhale escaped Twilight’s lungs. “Alright, then. So we’re all good. This is something we can talk about.”
Applejack idly traced the right angles of the picnic cloth before her. “Well, if we’re cuttin’ through the manure, I s’pose I’ll just ask: If the mood was right an’ all, would ya two ever consider… tryin’ it fer real? With us? Just once, to see what it’s like?” Slowly, her gaze lifted to take in the Canterlot-born siblings. Eventually, her sight moved past Twilight and followed the toned curves of Shining Armor’s frame; a trained, refined, disciplined stallion in peak physical condition; friendly, yet commanding and regal.
In a mirror gesture, Twilight’s eyes focussed on the pony behind Applejack, drinking in his muscled crimson bulk with an awakened shimmer; a form so different, so much larger than her own brother, yet tempered by gentleness and kindness, less varnished perhaps, but undoubtedly stronger. “I... I might, if... if everypony were okay with it... I mean, as long as we're all informed and consenting, then there's no problem.”
“Yeah, I– I guess I’d be okay with it, too,” the farmpony said nervously, twisting her neck over to pose the silent question to her relation.
“Eeyup.” Big MacIntosh’s sedate eyelids never gained altitude.
Shining Armor seemed to take a moment to consider the proposal, studying in turn his own sibling, and the pair of siblings a few paces away. At last, his lips pulled up into a shy grin, and he diplomatically offered, “I think I might like that.”
“So, I guess if everypony agrees... we could... set up a time? Another date later this week?”
“How ’bout right now?”
Those words, spoken in the larger stallion’s sonorous southern drawl, forced another pause in the world. Fortunately, everypony seemed to be getting used to such interruptions, and all recovered after only a minimal delay. It was Big MacIntosh’s turn to blush, turning his already-red coat positively incandescent.
“Um... right now?” Twilight questioned. Her muscles tensed fearfully, yet her tongue brushed her lips in obvious desire as her hoof stroked Shining Armor’s foreleg.
“Uh, sorry,” the red stallion replied.
“No, it’s... it’s fine... I mean, heheh, there’s no time like the present right? I just assumed...”
“Twilight,” Applejack interjected, giving her brother a quick glower of disapproval, “nopony’s got to do anythin’ they don’t want.”
“No, I know that, of course! I was thinking mostly about everypony else, taking some time to think it over.” She faced her brother. “Is this something you need to discuss with Cadance beforehoof?”
Shining Armor dithered. “Uh, strictly speaking, no... It’s just that...” A pause.
“What?”
“I don’t keep any secrets from Cadance,” he explained. “Anything that happens here, she’ll know about. That’s non-negotiable.”
“Sounds fair ta me,” Applejack said after a moment of thought.
Big MacIntosh nodded simply.
“You’re fine with that, Twi?”
“Are you?”
“I am if you are.”
“I’m fine to go if you’re all fine.”
“Well, I’m fine if everypony else is fine.”
“So... does that mean everypony is fine?”
“This is going to be a painful road if we keep up like this,” Shining Armor suddenly declared, putting the floundering exchange out of its misery. “There’s... uh, a trick I learned in the Guard, that every good commander knows. Plus, Cadance does the same thing to me when she wants to talk me into something I’m unsure about.” He smirked knowingly for a moment, then inhaled through his nose and lifted his chin authoritatively. “We’re talking about swapping siblings for the purpose of having sex with a new pony. Does anypony here not want to do this, right now?”
There was quiet. Nevertheless, the blushing, nervous, yet smiling faces told all involved what needed to come next.
Applejack fiddled with her Stetson. “So, uh... are we really goin’ through this? An’ we agree things won’t get all weird after?”
Twilight’s bobbed her head once to confirm. “Sure. We’re all rational, mature adults. If anypony’s uncomfortable, we can stop at any time. And no hard feelings if we do stop, right?”
“Right.”
“Sure.”
“Eeyup.”
A few seconds elapsed.
“Alright, so, uh...” Twilight’s brows furrowed. “I’m not really sure what the protocol is for partner-swapping. The last book I read on the subject didn’t go into specifics. We should probably decide who gets to start.”
Gently, her brother lifted himself onto his hooves, being careful to deposit his sibling into the grass with an assured embrace. “I guess I’ll take the lead from this side,” he suggested. “Big MacIntosh?”
With his trademark lone word of agreement, the other stallion slid out from underneath his own sister, locking eyes with her for a split-second, a wealth of unspoken words and assurances flowing between them. The two Apples kissed.
Not to be outdone, Shining Armor did the same, whispering a simple yet profoundly meaningful, “I love you” to Twilight.
“I love you, too,” she replied. Her ears flicked in anticipation and her muzzle beamed. “Have fun.”
With a slow, assured gait, and adoring looks back, both stallions left their sisters where they were. Their eyes shimmered and gleamed. They both swallowed.
They met head-on in the middle. They scanned each other, first with their eyes... then their noses. They sniffed. They nuzzled. They kissed. They embraced. They fell onto the grass.
They started frotting.
And that was only the start.
“Holy fuck, they should call you Huge MacIntosh!”
“Eeyup.”
Above them, two mares looked on in expressions of mixed horror and stupefaction.
“This... wasn’t what you had in mind, was it?” Twilight queried, her lower left eyelid twitching.
“That ain’t all you got, is it, soldier?”
“Heh, just watch me...”
“Uh... nope,” Applejack answered weakly, screwing up her face with a bit of tongue sticking out.
“I always liked the strong, silent types. Not much comes out of your mouth, so let’s see how much can go in.”
“Mmmphhh...”
Slowly, torturously, the mares’ eyes tore away from the all-male tangle of fornication, and found each other. They held that gaze for a seemingly interminable length of time as increasing cries of passion sounded just a tail’s reach away.
“Fuck, Shine, don’t hold out on me...”
“I don’t plan to...”
“Ah, what the hay!” Applejack cried, and tackled Twilight.
Author's Note
I decided that I needed a story to celebrate the spirit of April Fools' Day.
Back in 2013. 
I kid you not. This story was actually started March 3, 2013, while I was still riding a bit of a high from the unexpected successes that were "Complicated Relations" and "On The Importance Of Spelling". Unfortunately, just short of hitting the 1000-word mark, I hit a block, the deadline passed and this story languished on my hard drive for over a year.
A couple of weeks before April 2014, I decided to revive it, but this was in the middle of a pretty deep writing rut, and progress was almost nonexistent. As of midnight, March 31, 2014, the word count was around 1250.
Then, on April 1, through some perfect mix of anger, frustration, inspiration, nice weather, and the eight planets aligning, I decided to sit down and write. It was painful, it was past midnight in my timezone (so technically April 2) when I published this story, it was full of typos (as there had been no time to send it to any pre-readers) and it was missing a few pieces I had wanted, but it was something.
And it had a joke at the end.
And that, boys and girls, is how Equestria was made. 
