Author's Note

Content Warnings - feral ponies, princest, dream sex, Dom Luna, clone gangbang, ‘public’ sex, light inflation, bukkake, Pinkie being Pinkie.

To Fill a Princess’s Cavities

“For the last time, I do not need to go to the dentist!”

The Princess of the Sun glared down at her younger sister, scowling.

Luna returned her aggravation in kind. "Sister, since our return thou hast partaken of nothing but sweets. Thy teeth are surely rotten."

“No they aren’t! I am perfectly fine. I am a princess, and princesses do not get cavities.”

Luna raised an eyebrow, her horn lighting as she summoned an ice cream bar and shoved it into Celestia’s mouth.

The reaction was immediate. Celestia's eyes shrunk to pinpricks as a sharp pain radiated through her muzzle. Tears streamed down her cheeks as she spat out the impossibly cold treat which tortured her poor muzzle.

“T-that's not fair Luna!” Celestia whined as she held her muzzle, trying desperately to soothe her aching teeth.

Luna snorted. “For Starswirl’s sake sister, thou are more stubborn than the ass keeping the gardens!”

Celestia pouted in a very un-princess like manner. “B-But Luna…”

“No buts Tia, unless it is thine own sitting in the dentist’s chair.”

Celestia pouted more, rubbing her cheeks and muttering under her breath.

Luna stood her ground for only a moment before sighing and wrapping her wings around her older sister, “Oh sister dearest, we apologize for being so harsh, but thou really must take care of thyself…”

Celestia whimpered quietly and snuggled into Luna’s side. “No...No, you are right sister. It’s just...I’m scared of the dentist. The thought of somepony prodding around in my mouth, when I am awake no less is... unpleasant to say the least.”

“We do not know much of modern dental techniques, but what if we could convince the doctor to let thou be asleep? We could then enter thy dreams and help take thy mind off of the procedure.”

Celestia blushed. “Y-you would really do that for me?”

Luna smiled and kissed her sister softly. Once she pulled away, she licked the tip of Celestia’s muzzle. “Of course sister, we wish thou to be healthy and happy.”

Celestia hugged her tight. “Alright sister, I’ll set up an appointment.”

~~

The day arrived and Celestia, having barely slept the night before, paced around her darkened room. She had been there the entire day, locked away as she contemplated the upcoming appointment. Her body was bare, her regalia stashed away still. She found herself unable to put them on, almost angry at the gold and pristine apparel.

She stopped in front of a mirror, her ears down as she took in her ragged appearance. Her mane moved limply, almost stuttering in its normally fluid movement. The princess snorted and turned away from her reflection.

Celestia walked over to her window and opened her blinds, allowing the early evening light to wash over her. The princess sighed deeply as her mane and tail perked up a bit, relishing the soft and glistening light. She gently reached out to the sun with her magic, feeling even more warmth wash over her, calming her nerves as she nudged it below the horizon for the evening.

She was startled by a knock at the door, shutting the blinds quickly and diving under her bed covers. Surely now she wouldn't have to see the cursed dentist and have her teeth meddled with.

The knock repeated but Celestia did not move, even burying herself deeper in the plush blanket when she heard the door opening.

The hoofsteps told Celestia it was her sister, the deep sigh following confirming it. “Oh sister, must we really do this?”

“I have no idea what you are speaking of sister.”

Luna rolled her eyes at her sister’s muffled reply, jerking off the blanket in one quick movement. Celestia whined and kept her face firmly pressed into the sheet, even bringing her wings to hide her head.

Luna leaned over and nipped Celestia in the flank, right where she knew she loved it. Celestia yipped and shot upwards, “Lunaaaaaa…”

“Celestiaaaaaa.”

Luna smirked as she responded in the same whiny tone her sister had taken. Her sister was not amused and stuck her bottom lip out in a pout. “Sister, thy dentist is setting up as we speak, thou needst to stop being such a foal.”

“Fine, fine...You know, if you told me what awaited me in the dreamscape I might be more motivated to go…~”

Luna deadpanned her sister, even as she gave her best puppy eyes. Slowly, a smirk spread across the younger’s lips, “We would hate to ruin the surprise. Rest assured we are confident thou shall enjoy it.”

Celestia pursed her lips. “Oh fine then, keep your poor sister in the dark.”

Luna snickered and pecked her on the cheek. “Aye, we shall.”

Celestia was about to retort when a soft knock came from the door.

“Your highness? The dentist is ready for you.”

Both sisters sighed, the elder one’s heavier.

Luna nuzzled her sister and stood up. “Come along Tia, we do not wish to keep thy good doctor waiting now, do we?”

Celestia made a noise indicating otherwise, earning her a slap on the flank from Luna’s wing.

She yelped and hurriedly stood, “Okay, okay, I’m going, I’m going.”

“Soon thou shalt also be cumming," Luna whispered into her ear, grinning as she walked past, batting her nose with her tail.

The guard standing outside did not make notice of Celestia’s bright red face, though Luna caught a slight twitch of his lips before he forced it back into a perfect poker face.

He bowed. “I have been asked to escort you both to the surgeon’s room your highnesses.”

“We thank thee, good sir. Please, walk us to our destination. We shall make sure Celestia comes forthwith.”

A twitch of the guard’s ear at Celestia’s quiet, accusatory muttering aimed at her little sister, was the only movement he made before standing up and turning down the hall.

Luna walked with a wide smirk, her horn lighting ever so often to poke and tease at Celestia’s flank, much to the elder alicorn’s embarrassment. Any guards they passed kept their impassive gaze forward, slight twitches being the only indication they noticed what was going on.

Not that any of this was a surprise to them. However, they were all sworn to never speak of anything that occurred between the sisters.

After what seemed like an eternity, they arrived at the hospital wing, usually intended for the servants and guards of the castle.

They walked through the hall and into a sterile room. It held a chair with a light and mirror fixed above it, a table covered with dental tools, a couple rolling stools, as well as an armchair set in the corner. Celestia shuffled her hooves as she hesitantly made her way to the chair, laying down in it and attempting to relax.

Luna nodded at the guard, “Go tell the doctor we are ready.”

He saluted before trotting away.

Luna then turned towards Celestia and closed the door, coming up to the chair and nuzzling her. “All will go just fine sister, it shall be over before thou knows it.”

Celestia whimpered, opening her eyes and staring longingly at the door.

Luna raised an eyebrow as her sister’s head peeked over the chair, her body slowly moving into position as if to pounce out of the chair and run away.

“Sister…”

Celestia winced at the warning in Luna’s voice, settling back into the chair and sticking her tongue out. “I wasn’t gonna do nothing…”

Luna rolled her eyes and stifled a laugh - her sister could be quite foalish when it suited her.

“Your highness? May I come in?”

Luna turned towards the door and opened it with her magic. At the same time, dark blue tendrils tethered Celestia to the chair. “Please do, kind doctor, our sister is ready.”

The doctor, a middle aged unicorn stallion of grey coat and silver mane walked in, his cutiemark a toothy smile. He walked over to the chair and smiled at Celestia, his lips downturning for only a second, as if debating if he wanted to comment on the magic binding one of the rulers of Equestria.

One look at Luna and his decision was made.

“Princess Luna, Princess Celestia, it is a pleasure.”

He bowed slightly before turning his gaze to Celestia, “Now, I spoke to your sister about the anesthesia, and while it is unusual during light dental work, there is no danger in doing so. Before I cast the spell though, I would like to look around in your mouth while you are still awake, will that be okay?”

Celestia’s ears flattened against her head as she looked pleadingly at her sister, but found no mercy. With a grumble she opened her mouth, resting her head back against the chair, maintaining the air of a prisoner about to be tortured.

The doctor stepped closer, levitating a small mirror into her mouth. He hummed softly to himself as he worked, tapping her gums and teeth occasionally, seeming to take silent note of every wince and whine of pain.

“Eyup, you definitely have some cavities, Your Highness. They aren’t too severe though, I’ll have you fixed up in no time! Princess Luna, normally I would cast a sleeping spell but I am unsure of what adjustments need to be made for an Alicorn, would you mind terribly?”

“Nay doctor, we were expecting this.”

“Thank you kindly.”

As the dentist turned away to prepare his tools, Luna stepped forward and pressed her forehead against Celestia’s. Her horn glowed a soft blue as she quietly counted down from 10.

At eight, Celestia’s breath deepened.

At five, her eyes began to flutter.

At three, she was sound asleep.

Luna kissed her forehead and walked over to the armchair, relaxing in it as she cast a spell upon herself. “We shall see thee soon, good doctor.”

“Of course Princess, sleep well.”

~~

Celestia opened her eyes, looking around to see she was in her room. Well, the dreamscape’s version of her room at least. She smiled and walked to her large bed, flopping down on the silken sheets and soft cloud mattress. She felt the bed depress beside her and turned to see Luna laying next to her. Celestia shivered, anticipation and excitement starting to buzz through her.

It had been quite some time since the sisters had played together, even longer since they’d done so in the dreamscape.

Luna nuzzled her sister, pressing her lips firmly against her neck, enticing a soft coo from Celestia. Luna pressed forward, a soft growl rumbling in her throat as she peppered the exposed flesh with little kisses and gentle bites.

The reaction was much less subdued, a gasping moan drawn forth as shudders danced down the elder sister’s spine, heading straight to her rapidly dampening marehood.

A plea was forming on Celestia’s tongue, for Luna to stop being so cruel and keep from teasing her too long. Luna knew her sister well though, and quickly moved to capture Celestia’s lips in a deep kiss, effectively killing the pleas.

Celestia whined against her sister’s lips, squirming on the bed as Luna rolled her onto her back and pressed down into her. There was something about Luna when she was extra dominant that drove Celestia absolutely crazy. Maybe it was that it was Celestia was the older sister? Or maybe because she loved to be submissive? Such questions would have to be answered another time as Luna pulled away and growled again.

“Whatever shall we do to thee? Mayhaps we should ravage thy holes until ‘Celestia’ is but a moaning whore, naught able to speak but only to beg for cock. Maybe we should strip thee of thy magic and throw thee to the raging timberwolves of The Everfree.”

Luna paused, smirking as her sister squirmed and whined even louder. She found it fascinating just how submissive her elder sister was, dripping wet after but a few moments of ‘speaking dirty’. “Or…”

She drawled out, leaning into Celestia’s ear and biting it. “Perhaps it is sufficient to remind thee who truly rules Equestria~”

“P-please sister~! S-stop teasing meee…”

Luna snorted, drawing away from her ear and climbing off of Celestia, sitting at the end of the bed with her legs spread before her. Her horn glowed and an especially dark patch of shadows ran down her body to her nether region, coalescing into a solid mass which stirred before stilling. After a moment, Luna’s magic dissipated, leaving a proudly erect member.

Celestia licked her lips, panting as she scrambled to get her hooves under her and crawl to the beautiful tool before her. Luna held a back hoof to her muzzle, stopping her just short of what she craved. “Tsk tsk sister, hast thou forgotten thy manners already?”

Luna chuckled at the whimpering response, her magic pulling Celestia’s tail and rump upwards, leaving her no choice but to grovel.

“Aye, better, but something is still missing…”

Celestia gasped as Luna’s magic wound around her throat, calling into form a simple black collar. A small silver tag hung from it, blank for now.

An almost physical change swept through the alicorn, her head lowering and her body seeming to become smaller. The collar was on and Princess Celestia was gone. In her place was Tia, pet, slut, bitch; whatever mistress deigned to call her tonight.

“Much better, wouldn’t thou agree, Bitch?”

And there it was, her name for the night. The blank tag flashed, now bearing an elegantly scripted word; Bitch. The submissive Princess shuddered, the word rolling down her spine. She licked her lips and nodded. “Y-Yes mistress, this...this bitch is happy to s-serve you.”

Luna’s hoof moved, but she stayed still. She hadn’t been ordered forward yet; if she moved she would be a bad girl, and bad girls got punished. Celestia, no, Bitch, didn’t want to be punished.

Moments passed like years, sweat starting to trickle down her neck as she salivated over the delicious cock before her. She could smell the musk rolling off of mistress, the tanginess of it creeping into her nostrils and overwhelming her senses with it.

She let out a needy whine, opening her mouth wide and sticking her tongue out. She was so close and mistress was being so mean…

“Good girl, thou shalt have thy reward in but a moment. We do believe a change in scenery is necessary.”

Bitch tilted her head, wondering what her mistress would do. “Close thine eyes.”

She hesitated only a moment, hearing mistress’s horn light and feeling magic dance across her body. There was a soft ‘pop!’ And then all was quiet and still.

Bitch kept her eyes closed, she could definitely tell she was somewhere else but she couldn’t quite figure out where. She was standing up now, wood beneath her hooves. A steel stock was locked around her neck and forehooves as a spreader bar and chains kept her hind legs spread and hooves on the ground.

Her ears flicked as she heard muttering and shuffling. A deep blush reddened her cheeks as she realized she was somewhere ‘public’.

She shrieked as a hoof spanked her flank, her fur rippling under the impact. “Citizens of Ponyville! We welcome thee to this, the day of the Summer Sun Celebration! As thou can see, this year’s centerpiece shall be none other than the Princess of the Sun herself! Or, as we, and soon thou shall know her...Bitch.”

Bitch whimpered as the audience stomped their hooves on the ground. Shame turned her white coat pink, but she could not deny how utterly turned on she was getting from this.

The hoof that struck her flank groped her now, mistress continuing to speak to the crowd. “Thou shalt have the pleasure of watching us use ‘Princess Bitch’ here until we are satisfied. Please, feel free to pleasure each other as we slake our lusts on this whore.”

Mistress withdrew her hoof from her flank and trotted around her, rearing up and placing her hooves on the stock. “Eyes open.”

Bitch’s eyes fluttered open, pupils widening as her gaze was dominated by the dark blue head of a cock. Her mistress’s cock.

She began to drool immediately, opening her mouth wide without second thought. Mistress chuckled loudly, thrusting forward just enough for the tip to rest in Bitch’s mouth.

Mistress shuddered as her bitch moaned loudly, lashing her tongue around it and drinking the drops of pre that flowed forth.

The cock slid forward into her mouth, and so Bitch flattened her tongue, taking deep breaths through her nose.

“Yes, good Bitch, suckle our cock like a foal at the teat. Thou shalt have thy reward.”

A gasp rippled through the crowd but Bitch was focused on her task. Imagine her surprise when a second cock prodded at her pucker. Her eyes widened, choking a questioning whine around the member occupying her mouth.

Mistress laughed and pet her mane. “Worry not dear bitch, we said thou was to be rewarded. Do not despair, ‘tis not a commoners cock that pokes at thy backdoor.”

Mistress’s horn flashed, bringing into existence several mirrors, which she adjusted until Bitch could see that there was a second mistress behind her.

Bitch moaned loudly as her pucker was spread by the clone, the vibration causing mistress to hiss in pleasure. Bitch’s heart leapt for joy at the sound, happy she was pleasing mistress.

She moaned more, trying to twist her head side to side to please her mistress even more. At her rear, the clone had bottomed out, spanking Bitch's flanks and crying out as her hole tightened from the impact.

Hooves wrapped around her barrel from under her, hind legs locking around her hips as a third clone was brought into existence, bringing their cock to her sopping cunt.

Bitch was lost in a sea of pleasure, her body shaking as she was pounded viciously from every hole.

Mistress growled dominantly as she began to truly fuck her toys throat, Bitch only able moan as her eyes rolled into her head.

The clones taking her rear holes had worked into a seesawing rhythm, the one in her ass would pull out just as the other slammed into her cunt. Back and forth they worked the alicorn, seeming to not care for her pleasure but simply using her.

She gurgled around mistress's member in her mouth, opening her eyes enough to plead for permission. Mistress grinned and all at once the three cocks slammed into her spasming holes.

Mistress leaned down and bit her ear roughly. "Cum."

Bitch would have screamed if she could, but wasn't able to even breathe as mistress’s cock flared in her throat. The clones flared in their respective holes, and they came.

Bitch shook in her bonds as her own orgasm crashed over her, her ass and pussy tightening and spasming even more over the cocks as they filled her every hole, pumping her full.

She had no choice but to take every drop of their seed, her stomach, ass, and womb quickly becoming filled; even a bit beyond capacity. Bitch groaned weakly as her stomach distended slightly, her legs giving out and only being held up by her bonds and the clones behind her.

After what felt an eternity, Bitch on the verge of passing out from lack of air, all three cocks withdrew from her.

She gasped and panted heavily, drawing in the precious oxygen. Her mind was kinda fuzzy, but after a few deep breaths she could comprehend better what was going on. Her ears perked at a peculiar sound, looking up to see her three mistresses jerking off.

She gasped happily and obediently opened her mouth as wide as she could, closing her eyes and patiently awaiting their gift of seed. She was surprised to feel the tip of one on her tongue, guessing from the lack of taste from either of her rear holes it was her mistress and not a clone. “Eyes open Bitch.”

She obeyed, looking at mistress with joy as she felt the telltale twitches of a cock about to cum on her tongue. Mistress grunted as she orgasmed again, her seed hitting the back of Bitch’s throat and filling her mouth quickly.

Warm cum splattered either side of her neck and face, staining her already white coat an off white. Bitch moaned at the feeling and struggled to keep up with swallowing her mistress’s gift - she was a good slave after all.

Bitch wrapped her mouth around mistress’s cock, suckling on the tip as she savored the taste. Soon her mistress was finished, slowly pulling back until she popped free of Bitch’s mouth.

Their second orgasms spent, her mistress stepped back, allowing Bitch to work on swallowing the rest of the cum in her mouth.

Once she was done she flicked her tongue around to collect what was splattered on her cheeks. Only when she had cleaned as far as her tongue would reach did she open her mouth wide to show there was none left. Mistress smiled and let her mane. “Good girl, thou hast performed admirably.”

Her horn lit and the clones disappeared. Next to disappear was the bonds holding her up, the cum stained Alicorn flopping gracelessly onto the stage. Luna dissolved the collar around Bitch’s neck, returning her to Celestia.

Luna grinned as she pecked Celestia’s cheek. “Didst thou enjoy thyself?”

“Mmhmm…”

The sound of a hoof digging through popcorn interrupted the calm quiet that had overtaken the square. “Woweeezowie, that would have been a much better use for my clones! Oooh, I bet Dashie would just love that!”

Celestia paled at the sound of one of her subjects, the party pony Pinkie Pie. She slowly raised her head to see the pink mare wink at her, “Thanks for letting me watch Luna, that was an even better party than I thought it would be!”

Pinkie pulled an obscenely large clock from her mane, gasping. “Oh! It’s time for gummy and I’s 9:30 cupcakes! Bye princessesesses!”

Pinkie popped out of the dream realm, leaving a chuckling Luna and mortified Celestia. “Luna…”

The younger sister whistled innocently, lighting her horn. “Oh look at that, thy procedure is finished. We wish thou a good night’s sleep dear sister, We must attend to the rest of our nightly duties, ta!”

~~

Celestia jerked awake, moaning in pain as the soreness in her jaw quickly made itself present. She looked around, finding only the dentist cleaning his tools with a cheery tune. “Ah, you are awake your highness. How do you feel?”

A million answers swirled through the rulers mind, ranging from eloquent to straight cursing.

“I’m fine.”

~~

Celestia groaned as she stretched out in bed, hazy memories of the night before forming. The doctor had given her some care instructions and pain killers and then she somehow made it to her room to crash out.

She gently rubbed her cheeks, attempting to ease some of the residual pain of having somepony poke around your mouth.

She eventually rolled out of bed and checked the time, making her way to the window and lighting her horn, bringing the sun up and officially starting the day.

The rest of Celestia’s morning was fairly mundane. She headed to the kitchen to make breakfast, set the table, and awaited Luna’s arrival.

“Ah, good morrow dear sister, we thank thee for preparing our morning meal.”

Celestia nodded serenely as she lifted her smoothie glass to her lips, sipping at the strawberry-banana drink.

A soft ‘pop!’ and displacement of smoke startled her, glancing to her side to see a scroll. Luna tilted her head, “Twilight?”

“It appears so.”

Celestia opened the letter as she took another sip, something she soon regretted as she did a spit take. Her smoothie splattered against Luna as she came to her side to see the letters content. She blinked as Celestia gasped for breath, shakily holding out the letter for Luna to read.

“Dear Princess Celestia, w- I had the strangest dream last night involving you and Luna. I am unsure if I was supposed to see it, as it was very intimate...”

That was as far as Luna was able to get before laughter burst out of her.

Celestia moaned and hid her face in her hooves, muttering. Luna sniggered and elbowed her sister, “Hmm, mayhaps we should invite her to join us next time~”

Celestia shot up and glared at her sister, before an assortment of fruits levitated in her magical grasp.

Outside the dining room, two guards were startled awake by the doors slamming open, Princess Luna running out and strangely covered in fruit. More fruit flew after her as Celestia soon followed.

The guards chuckled and shrugged at each other. What happened between the sisters was none of their concern, and even if it was they were sworn not to speak of anything they say or hear occur.

Besides, watching Celestia chase her younger sister with fruit was rather amusing.