The Edge of Eternity,

by Horatio Horseblower

Rating: mature
Tags: Slice of Life, My Little Pony: Friendship is Magic, Princess Luna, Drama, Porn, Princess Celestia, Sex, Twilight Sparkle
Length: 5934

Luna is upset that their retirement has to be postponed. Sensing her tension, her dear sister takes the opportunity to help 'relieve' her of some stress.

Luna is upset that their retirement has to be postponed. Sensing her tension, her dear sister takes the opportunity to help 'relieve' her of some stress. As the only two immortal princesses, who better to turn to for such comforts.

Written for the for the April Wincest Contest

TAGS: Incest, Existential horse sex, drama, the concepts of immortality

Published 2019-04-30 05:20:01 UTC
Last updated 2019-04-30 05:20:01 UTC

is always just out of reach.

"Equestrian treasury and tax codes, military structure and strategies," Twilight muttered to herself in growing urgency, "alliances and treaties of trade. Where is it?"

The frazzled alicorn trotted though the halls of Canterlot Castle, her horn glowing softly as she levitated several scrolls in front of her, each completely covered in finely written script. They were lists of topics she was here in Canterlot to discuss with Celestia in preparation of her and her friends ascending to their thrones. There were so many things about ruling a nation that she wasn't prepared for, so many questions. So many lists to make out of the questions. Thankfully, she had the third task well in hoof.

The scrolls were fifteen in number, covered in text front and back, and arrayed in a semi-circle in front of her, their ends dragging on the floor, giving the comical appearance to anypony nearby that a wad of paper was hovering down the hallway mumbling to itself. More than once another pony had had to duck out of the way, lest the distracted tumblescroll bumble into them unknowingly.

Shuffling and reshuffling the scrolls, trying to keep them from tangling, Twilight pulled another to the center and read it's title. "Yakyakistani dining etiquette and protocol? No."

So consumed in her search for the right scroll was she that Twilight did not notice that the door to the throne room was already open until she was strolling straight through.

"Ah! Here it is-" Another scroll was plucked out of its place and brought front and center. Its bottom trailing along the floor and getting caught underhoof. With an undignified yelp, Twilight tripped and flopped forward into the generous cushion of overly prepared lists.

"Twilight?" Came a familiar voice.

"Hello, Luna." As the pony tried to stand, she found herself tangled in rolls of paper. Trying not to tear any of them, she began to delicately extricate them from around her limbs. "Sorry, um, just a second."

Frustrated and embarrassed, her wings flared out, puffing the scrolls up and giving them two more limbs to land around. A glowing blue aura enveloped the pony as she felt herself gently lifted into the air, the scrolls each rolling up and being stacked neatly on the floor.

Once she was set back down, Twilight dusted herself off, trying and failing to contain an awkward giggle at her own expense. "Thanks."

Clearing her throat and regathering herself, Twilight looked up to Luna, sitting on her throne, the blue glow of her horn fading away as she released the last scroll. Notably, the throne beside hers was presently vacant.

"Good evening, Twilight." the princess nodded in greeting. "I'm sorry I could not attend to this meeting earlier. Today has waxed long. You said you had something to discuss?"

"Yes," Twilight confirmed. "A lot, actually. There's so much I need to ask you and Celestia about running a nation. Is she here?"

"She is not," Luna answered flatly.

The unexpected abrasiveness of the answer caught Twilight off guard enough that she was uncertain whether or not it was intentional. Ignoring it, she raised the scroll off the top of the pile and levitated it over to Luna.

The Princess took hold of it in her hooves and partially unrolled it, raising an eyebrow and reading the first line of text aloud. "Canterlot septic infrastructure?"

"Probably not the best to start with." Twilight forced a smile and began to levitate several more scrolls in order to find the one she'd been searching for before. As they were once again spread out in front of her, blocking her view from Luna, she had to pause for a moment. Between the papers, she saw Luna turn to look out the window and give what looked like a long, wistful sigh.

Lowering the lists enough to peak over their tops, she asked "Is something wrong."

"Hm?" Luna blinked, collecting herself. "No. It is nothing."

With the princess on her throne and Twilight all the way at the foot of the stairs approaching it, it was hard to tell, but she could swear her eyes looked a little red. Not just red, but with a telltale puffiness around the edges, the bottom lids slightly moist. As if to confirm her suspicions, Luna gave the slightest sniffle, her hoof twitching as she resisted the urge to wipe at her muzzle.

As the princess of friendship, Twilight had put a lot of study into the body language of equestrians to make up for her lack of more natural experience during her more anti-social days, and she could tell well enough when somepony had been crying, or trying not to.

Taking a softer tone, she began to inquire, "Princess Luna..."

"It is nothing." Luna insisted, cutting her off. Frowning at her own rudeness, she tried to apologize. "Forgive me, but you would not understand, and the time it would take to explain would merely exacerbate the issue. I will be fine, given time. I wish not to speak of it."

Twilight gave a shallow bow. "I'm sorry. I didn't mean to intrude."

She could hear a set of heavy hoofsteps entering the room before their owner spoke, interrupting the moment. Her flowing mane was just coming into view when her mentor spoke.

"Ah, there you are," Celestia smiled at her most promising student. She then turned to her sister, the corner of her lips twitching downwards for just long enough for Twilight to notice. "I'm sorry for making you wait, sister. I had never seen two ponies so determined to argue for mining rights."

"It is resolved, then?" Luna asked, almost as if forgetting that Twilight was there.

"It is." Celestia confirmed. "The Silvertongue family will mine on the river's west bank, and the Copperheads on the east, just as before, and the former will pay a portion of their profits in fines for attempting to divert the flow of the river."

Luna gave a huff and looked back to the windows, like she had only heard the first few words. "It is all so tiring."

"Indeed." Celestia turned back to address their visitor. "It's getting late. I know you had a lot to ask about today, but this meeting came up unexpectedly. I'm sorry to ask, but can we postpone this until tomorrow?"

The princess of the sun's smile was still firmly in place, but her lips were too tight, too strained. Twilight could tell that she was forcing this for some reason. Glancing out the window, she could see the sun was indeed setting. For how long it would take to go through even a fraction of her questions, it was probably best to wait until morning.

"Not a problem." Twilight could tell that something was the matter, but knew not to press it.

"Then we are adjourned," Luna deadpanned. Flaring her wings, she alighted from her throne, landing at the base of the steps and calmly walking to the door, giving a simple "Twilight" as she passed by the smaller pony.

About to leave, herself, Twilight was stopped as Celestia spoke. "Hold a moment."

Once they were alone, Celestia began walking out as well, gesturing for her student to follow her. "Walk with me."

At her mentor's direction, she left the pile of scrolls where they lie, and obediently took a place beside her. They walked a full minute before Celestia spoke.

"Allow me to apologize for our rudeness." Celestia stopped a moment in front of an ornate tapestry. "Mine for being so late, and my sister's. She doesn't mean anything by it."

"I don't mean to pry," Twilight could not help but ask, but she felt close enough with this half of the royal family to not feel too intrusive for it, "but is everything all right?"

"She will be." Celestia paused again before explaining further, the forced smile evaporating, her tone more somber. "She was making plans for our retirement. The first thing on the list was a trip to the Great Library of Marexandria."

Twilight waited a couple seconds for a further explanation, confused. When none came, she pointed out "But didn't that burn down somewhere around fifteen hundred years ago?"

"Correct." Celestia gave a tired sigh. "Today, not even the city remains."

"I don't understand." Twilight puzzled over this. "She was sad because it burnt down? But that was ages ago."

"No," Celestia shook her head, "she was sad because she had forgotten. Forgotten, and then remembered."

Celestia ran a hoof over the tapestry beside them. "She always loved their artwork. As hard as we tried, we couldn't put out the flames. So much was lost."

"You were there?" Her student pointed out as much as asked. "But how did she forget?"

It was almost a half minute before her mentor responded, weighing her words as she absently stroked the hanging fabric. "Tell me, Twilight, do you consider yourself to be a pony with a good memory?"

The younger pony could tell when her mentor had shifted into a lesson. Going along, she answered honestly and directly. "Yes, I do."

Still not looking her way, her attention on the tapestry, Celestia asked. "What did you eat for breakfast nine days ago?"

"What?" Twilight asked nonplussed, having to think on it. "Ummm...oh, I know. I skipped breakfast because...wait, no, that was ten days ago. I...I don't know, but that's hardly the same thing."

"You're right." Celestia stopped rubbing the fabric, "Another question: why don't you remember?"

"Because it wasn't important," Twilight explained academically. "Our brain's don't store every bit of information or memory. If our brain's can only store so much information, little stuff like that isn't worth keeping beyond short term memory. In long term memory, it would only be garbage data."

"As for the important memories," Celestia pondered a moment. "Do you remember when I first took you as my student? The ceremony?"

"Of course" Twilight smiled as she recalled it. Her parents in the front row, beaming with pride. "It was one of the greatest days of my life. I'll never forget it."

Another simple question. "What month was it?"

"Apri-" Twilight began to answer, but stopped herself as she had to think. "No...May? No, it was definitely April. It was, wasn't it?"

Celestia gave a thin smile. "I don't know, Twilight. I don't remember."

Connecting her questions together, Twilight felt a pang of sad offence at the implication.

"Don't be offended." Celestia could read her like a book. "Just as that day was a long time ago for you, the library was a long time ago for us. A memory that sinks into the mire when left too long, but close enough to the surface to be remembered when called."

Twilight thought on this for a spell.

"One last question." Celestia paused again, like the new question had gravity. "What is a second to you? A minute? An hour? Not how they are measured, but how you see them."

"I...I don't know." Twilight admitted. "It's not something I've really thought about."

There had to be a lesson in here somewhere, she just couldn't see it yet, so Twilight turned the question around. "How do you see them?"

Celestia's smile took on a more genuine slant as she got the desired answer. "Much differently than you."

The immortal princess tugged on the corner of the tapestry, inspecting its edges. Her horn glowed, and a neat little square of cloth was cleanly, surgically sliced from the corner. She passed the patch to her confused student. "See the fabric as time, every thread a year. How much do you hold?"

Twilight squinted her eyes and quickly counted the fine threads, taking the question literally. It was a small patch, more of a scrap, really. Once she had counted how many threads were in a smaller portion, it was simple math to multiply from there. "Eighty eight."

It occurred to her that this was not far off from the average life expectancy of a pony.

"How precious is each year." It was not a question. Instead, Celestia dug her hoof behind the tapestry and lifted it from the bottom, gesturing to the piece of artwork in its entirety. "And how much do I hold?"

Twilight tilted her head up, looking to the top of the fabric. There was no point in trying to count. She knew that Celestia was old. Ancient, even, but she truthfully had no idea of how old that was, exactly. Nopony did. To be confronted by it in such a way was daunting.

"Look to the middle of the piece, and tell me how clearly you see the threads." Celestia let go of the tapestry, changing gears again as she began to explain the lesson outright. "Listen, my faithful student. The longer you live, the more your perception of time...shifts. For a child, ten minutes in a corner can feel like an hour. For an adult, an hour is nothing, just a fraction of a day. For my sister and I, a day is not even a thread, just a strand."

Celestia levitated the patch from Twilight and placed it against the larger whole. "And for the newborn, still taking their first breaths, a day is beyond their comprehension."

Twilight said nothing, speechless at the concept of immortality presented in such a manner. It was both easy to understand, but beyond her grasp in scale.

"Goodnight, Twilight." Celestia's horn glowed again, perfectly mending the patch back into the tapestry until not even a seam could be seen. "Think on my words. We'll discuss this further in time."

Once Twilight bid her farewell, she departed to find herself some quarters. Celestia lingered, waiting until her student had gone from her sight and she was completely alone. Her attention turned once more to the tapestry. It was, objectively speaking, a beautiful piece of artwork, depicting a handsome stallion with a long, majestic sand brown mane, wide shoulders, and a square, solid jaw. Celestia herself had been the pony to weave it, but it had been so long ago that not even she could remember when she had made it or the name of its subject. All that remained was the vague memory that he had the warmest of smiles. Everything else had faded too far, to be beyond recalling.

Putting the issue out of her mind, Celestia turned away, starting down the hall, and then taking the first right, her path diverging from her student's. It didn't take long to reach her destination. As the day ended, the majority of the Castle's inhabitants settled with the sun, leaving only the compliment of night guards scattered here and there.

Arriving at her sister's chambers, Celestia knocked twice, and let herself in. Luna's chambers were spacious, just as her own, though while Celestia's favoured a brighter colour palate, Luna's chambers were of dimmer, deeper hues. Soothing, dark blues and deep purples. She was the Princess of the Night. It was only natural that her personal sanctuary reflected this.

In the center of the room was Luna, reposed upon a large, round cushion, facing away from her guest, her horn glowing brightly. On the room's far wall was a set of tall doors leading to a balcony that were as much stained glass as door. Through them, Celestia could see the moon beginning to rise into view.

"Sister," Luna greeted her, concentrating on the task at hand. It was rising faster than usual. She was impatient.

The princess was familiar enough with the hoofsteps of her sister that she had no need to turn and see who it was that had intruded so unannounced into her quarters. Few would be so brazen. She had not even opened her eyes to confirm it.

"You had Twilight quite concerned," Celestia said, quietly closing the door behind her.

"Was she, now." Luna remained focused on her task. A true conversation would have to wait.

"She was," she faintly smiled, just enough that her sister could hear the expression in her words. "I told her you were making plans to visit Marexandria."

"Wonderful," Luna scoffed. "No doubt now she thinks me alzheimic."

"Not at all," Celestia assured. "I explained to her just how that can happen. About how a life as long as our can cause this."

The glow around Luna's horn flickered as he almost took to her hooves. The moon outside halted in its ascent.

"I did not say much," Celestia was quick to curtail any concern on the matter. "Only enough to set the foundation for later. The point is, it's obvious you're troubled."

Luna settled back into place and resumed her work. "And how could I not be? 'Twas a fantastic library."

Celestia's smile inverted. Her sister had never been a good liar. Walking over to her, she placed a hoof on her sister's shoulder. "We both know something as minor as this isn't the problem. Tell me, what's bothering you?"

In truth, Celestia already knew the answer, but she knew her sister would rather say it herself than be told it by somepony else.

"You promised!" Luna blurted, accusing. "You said that this time we would retire. That we would finally carry it through, and now we are forced to wait yet again."

Celestia began to rub her hoof in small circles, trying to comfort her. They had both been looking forward to this, for far longer than Twilight and her friends could begin to imagine, delayed once again."And we will. I'll hold to my promise. We just need to be patient."

"I have been patient!" Luna just short of shouted. She cleared her throat, composing herself. "We have been very patient, waited for so long."

"And we can wait a little longer." The hoof moved to her shoulder blade, beginning to massage her lightly. "You need to relax."

Luna uttered a quiet harumph, but settled deeper into the cushion, not rejecting the offered massage. "I am relaxed."

"You're tense," Celestia softly argued. The statement was true both in terms of her emotions, and her tight muscles.

Celestia smiled despite herself as she rubbed her sister's back with practiced care. She had always been the big sister, more imposing by her greater size, and the more powerful magically, but feeling the taut muscles beneath her sister's hide revealed that Luna was the more physically gifted. No, not gifted. Such would imply that she had not needed to work for it, and Luna had strove to maintain a perfect, well toned physique.

Relenting under her sister's tender care, Luna slowly drew in a long breath through her nose, held it a moment, and let the tension begin to deflate from her.

Celestia's smile deepened, rubbing up and down her back. The moon's ascent slowed, it's caretaker no longer rushing its movement, taking her time to enjoy the moment.

"You're still tense." It wasn't a lie. Her sister's muscles were like taut steel cables. She was more bothered by all this than she had thought. Celestia dug her hoof in deeper, gently loosening the cords. "Better?"

Luna shuffled a little, getting more comfortable, answering with a soft mmmhmmm as she rested her chin on a pillow.

As anypony could attest, a one hoofed massage generally leaves the recipient sorely wanting. The side of Celestia's lips curled upwards as she decided how to address this. Raising one of her rear legs, she moved it over her sister, placing it down on her other side, straddling her lower back as she pressed both the hooves of her forelegs into her shoulder blades.

Luna instantly tensed back up, her ears perking as she gave a subtle start. Her head slowly raised, but she did not try and turn it to face her. "What are you doing?"

"Like I said, you're too tense," Celestia replied, coyly. She leaned forward, lying on top her, her stomach pressing against her back. "I'm just helping you get some"

She brought her muzzle close to her sister's ear, she finished her sentence with a whisper. "release."

"I'm concentrating." Luna said, her breath growing heavy. She did not, however, reject the advance, nor attempt to move.

Sitting back up, Celestia resumed her massage, starting at her shoulders, slowly working her way downwards. As she rubbed her hooves into the middle of her back, she slowly ground her hips against down against her.

Luna shuddered beneath her. "Now is not the best time."

Her sister grinned knowingly at her choice of words. Not 'stop', or any form of such a command, nor even a statement that it was not a good time, merely 'not the best'.

"Shhhhh." Celestia softly hushed. "Just relax."

"No." Luna finally rebuked, tensing up under her. Not trying to remove her, but making it clear that it would be no effort should she chose to. "I will not be manipulated. I am not some mewling filly. You promised that we would retire."

"And we will." Celestia stopped her gyrations, but continued with her more conventional massage. "But we can't do that while Equestria is under threat."

"Equestria is always under threat!" Luna flexed her shoulders, shifting Celestia further down her back. "There is always something. It's always Discord, or Sombra, or Grogar, or the Breezy invasion, or Discord again, or Abaddon the Despoiler, or-"

"Yes," Celestia conceded, "but this ti-"

"Or Sombra again!" Luna resumed, growing more emotional, "or the Paralgeus Plague, the Smooze, the Windigos-"

Celestia cut her off again, listing threats that were addressed so long ago that nopony but them would even remember them. "Or Beezen, or Catrina, or Somnambula, or Arabus. Yes, I know, it's always something, and each time we have had to wait a little longer."

"I'm tired of waiting." Luna huffed, defeated. "I'm...I'm tired."

Celestia paused. It was true, they were both tired. Tired for longer than either of them could recall. A weariness that no sleep could remedy. She gave a deep sigh, lying forward against her sister and hugging her around her stout neck. "As am I, but we've waited this long. What's a little longer?"

Luna gave a sigh even deeper than her own, relenting. "Very well. Just a little longer. And then..."

"Yes." Celestia nuzzled against the back of her head. "And then it will be done."

To her credit, Luna had maintained her concentration on raising the moon the entire time, the celestial body now halfway above the horizon, like a tarnished silver half circle.

The two of them lie there a long moment, letting the tension of their argument dissipate. It was broken when Luna perked up again, noticing Celestia resuming the grinding of her hips against her lower back.

Luna tried to look over her shoulder. "Wha-"

"Shhh." Celestia kissed her cheek. "I think now, is the perfect time."

Slowly, the older princess scooted backwards a bit so that she was no longer straddling her sister but sitting directly behind her, still lying atop her. Gradually, her hooves began the trip southwards, pressing between their bodies as they traveled a well known trail down her back towards her flanks. They stopped just above the dock of Luna's tail.

Celestia waited, and in a few seconds got the signal she wanted. A slight shuddering in her sister's hips. A catch in her breath. The subtle spreading of her thighs. A faint, familiar aroma. Smiling again, Celestia's hooves finished their journey, finding an aroused moistness at their destination.

The nature of their relationship was, for obvious reasons, not known to anypony but themselves. Were they to find out, most would judge them rather harshly, and not unjustifiably so, save perhaps for the Apple family. Their's was a bond deeply forbidden, but millennia old. One of consequences of immortality was the loneliness it could bring. For all their uncounted centuries, they had only each other.

It had not always been like this. Once, so long ago that not even the history books recorded it, when they were still young, Celestia had been married. He had been a wonderful stallion. A pony of legend for ages to follow. Poems were written, songs were sung, statues carved and great tapestries woven, but like all mortals, his time passed, as did he. As the eons marched on, the poems were forgotten, the songs went unsung, tapestries rotted, and statues eroded. Time erases even graves. Now, neither of them could even remember his name or his face. Only that he had the warmest, most charming of smiles. Forgetting something was the worst part of losing it. The only memory being that there used to be one.

In their unending, immortal lives, ponies came and went, their impermanent lives but fleeting flickers in a flame. In an ever changing world, they were each other's only constants. Their only pillars. Who else could they rely on for such comfort, on who else could they lean. Who else could they truly love.

Bringing her forelegs back up, Celestia stood, raised above her sister. Pressing her muzzle between her sister's shoulder blades, she began to leave a trail of tender kisses along her spine, each one just a little bit farther down. She slowed again, waiting as she shifted herself so that she was looking directly at her prize.

Celestia had always been the more patient pony, and she delighted in making her lover wait, if only to tease her just a little before beginning in earnest. Her foreplay had been refined since before the first stone of their castle had been set. It was a mix of art and science, honed to perfection. She had pressed all the right buttons. Now, she waited.

It was not long until she was rewarded.

"Celestia," her sister softly begged, both in voice and body as she winked.

Her sister didn't have to wait any longer as Celestia ran her tongue along the slit of her sister's opening. As she cooed and winked again, she pressed her muzzle against her, delving her tongue into her depths. A hoof was pressed against her bud, rubbing in little circles as she let out a soft, vibrating hum. Her ministrations elicited a drawn out mewl from Luna as she pressed her face into her pillow, opening her legs wider, bidding her further.

Celestia was a gentle lover. No, she was an artist, and her tongue was her brush, tenderly bringing a masterpiece to its culmination. How Luna managed to continue raising the moon during times like this always impressed her. More than once Celestia had sent the sun far off course when she was on the receiving end during a morning get together.

Removing her hoof, Celestia wrapped her lips around her sister's love button, softly suckling it as she flicked her tongue across its sensitive, sensual surface. As if on queue, Luna's hips shot up, her hind legs shooting out behind her as her thighs wrapped around Celestia's head, pulling her in deeper. There was no escape from the grip of Luna's muscular legs, not that Celestia would want it. She was exactly where she wanted to be.

Contrary to most pony's beliefs, the sisters did not need to move their respective celestial bodies across the entire sky. They merely raised them, sent them on their way, and caught them again once they reach the other horizon, resetting them for the next cycle. The glow around Luna's horn faded, finished with its task. Her sister could now have her undivided attention. Celestia smiled in anticipation so wide she could feel it.

The thighs around her head flexed, gripping her tighter as she rolled. Incapable and unwilling to resist such force, Celestia was rolled over onto her back, the maneuver finishing with Luna sitting straight up, on the knees of her hind legs, her hips clamped above her sister's face, which was now pointed upwards.

Celestia didn't pause in the slightest as her sister sat on her face, grinding herself down into her, welcoming her muzzle inside of her. Now that she was free of her nightly task, Celestia had needs of her own. She hummed harder as if she was clearing her throat, an erotic 'ahem' to grab her sister's attention as she spread her own legs in invitation.

Taking the hint, Luna lay down on top of her, hungrily clamping her mouth onto her sister's mound. If Celestia was an artist, Luna was an engineer. Her craft was practiced and mastered. Each tool at her disposal used to their upmost potential. And just as Celestia was gentle and tender, her sister was ravenous. Luna pulled her sister's legs wider still, demanding more access. Access she was readily given. Her tongue and hooves in constant yet precise motion as they sought to return the pleasure she had been given seven-fold.

They complimented each other perfectly. Where one had need, the other had everything they wanted. Any moans or screams of pleasure anypony might hear outside would be well dampened by each other's embrace.

This was not to say they had never been caught, but rumours tend to die back down after a generation or five. It 's easy to rewrite history when you predate any of the books. All it takes is patience.

Celestia could feel herself drawing close to the precipice, her ministrations growing rougher as she began to buck against her sister's muzzle. However, with her head start, it was Luna that arrived first. She shot back up, grinding herself harder and harder against her sister, greedily taking her muzzle as deep as she could as she rubbed her own bud. Unable to escape and unable to breath, Celestia committed to seeing the act to its fruition. Finally, Luna bit into her foreleg to stifle her voice as she climaxed, her entire body shuddering. The entire room took on a blue glow as her horn shimmered and sputtered like a flickering light.

And then Luna dismounted, leaving her sister lying on her back, waiting. She was far past willing to wait.

"Please," She resisted the urge to rub herself. "Don't make me beg."

Luna slowly, gingerly walked around her sister, settling down with her face between her legs, looking up the length of her body as she met her eyes. "Promise me."

In her near orgasmic state of mind, Celestia had to think a moment to clear the haze. "Whut?"

"Promise me," she repeated, slowly giving a single lick along her opening. "No more delays. This is the last time. Once this matter is done, we retire."

"Okay." Celestia relented.

"Promise," she persisted. "I want to hear you say it. That we'll finish what we started."

Celestia curled up into a semi-sitting position, lovingly caressing her sister's cheek. "I promise. No more delays. We'll retire, and then..."

"And then," Luna began to finish for her, "we can die."

Her promise accepted, Luna dove in, lapping and plunging her tongue into her, her muzzle pressed and rubbing against her bud. She was less ravenous, taking her time in apology for making her lover wait.

Celestia lay back, enjoying it, not caring to quiet any moans that escaped her.

There were many facets to immortality. If one was to ask somepony if they wished to live forever, many would immediately and foolishly answer 'yes'. Many more would think on it, then answer the same. A more shrewd pony might wonder at any caveats that might ruin eternity. There was the question of what happens if they're horribly injured or crippled forever. Some might develop a sudden fear of being trapped in the bottom of a mine-shaft or some other inescapable place forever. The more sensible might refuse immortality on the notion that it would get lonely, and only accept if they had someone to spend it with. Such romantics were the most foolish of them all.

For Celestia and Luna, they were well aware that all of these concerns were pointless. It did not matter if you were in good health, or physically free, or with the pony you loved. Living forever was a curse, not because of anything that might ruin eternity, but because of eternity itself.

As Celestia had explained to her most recent student in an unfathomably long line of students, the more time one experienced, the more their perception of it shifted, the more it changed.

Nopony knew exactly how old the royal sisters were, not even themselves. Where the common pony measured their lives in years and decades, they measured in millennia and vague ages, and they had long lost count of either. They had seen nations rise and fall, landscapes shift and reshape like the tides. They had been present for the sculpting of the moon and the rekindling of the sun.

Life itself was an unceasing blur of ever changing faces. By the time they remember the names attached to them, they had passed on, replaced and replaced again. Again and again and again and again.

It was all so very tiring. A tiredness that no impermanent rest could fix. Once Twilight and her friends had taken the mantle, the world would have no further need of the two of them. Their obligations as its protectors would come to a close, and they could finally end. Celestia only hoped that the six of them would not judge them too harshly once they discovered that the curse of eternity was to he passed onto them. In time, they would come to understand their desire to escape it, and would no doubt eventually make plans to do the same, themselves.

As ancient as the sisters were, old beyond number, the world had been ancient long before they were born. It had survived before them, and it would survive after them.

These were concerns for later. Nearing her climax once again, Celestia curled up and held her sister's head in her hooves, their eyes meeting lovingly. They had spent one eternity together. They would meet the next together, as well.

The edge of eternity was always just out of reach, but tonight, it was a little but closer.

Sensing she was near, Luna buried her muzzle and gave a deep, throaty hum. That was all that was needed to drive her over the edge. Celestia threw her head back and let loose a scream, uncaring as to whomever might hear it. Her horn burned brightly, illuminating the room with its brilliance like a flash bomb, fizzling out just as suddenly.

Panting, Celestia let herself flop down onto her back. Wiping off her muzzle, Luna slid up along her body until she was lying on top of her, wrapping her forelegs around her in a loving embrace. The room reeked of sweat and sex. Another problem for later.

Petting her sister's mane, Celestia reaffirmed her commitment. "I promise, sister. We'll be together forever. Wherever that may take us."

Outside the door to Luna's chambers, a scroll was dropped to the floor as the purple magical aura that had held it aloft fizzled out. Twilight stood there, hoof outstretched, foreleg twitching. She'd seen the moon moving erratically as it rose, and had come to see if something was the matter. She had just been about to knock on the door when she'd heard Celestia's orgasmic cry, and these were not Celestia's chambers.

"Eeeeyup." Twilight said to herself. "That's going in the vault."

Her horn flared, and for the third time since she'd known the sisters, she erased the last fifteen minutes of her own memory.

Author's Note

Thanks for reading. This has been the first lemon I have written.