Hard as Rock

by thathornypony

Rating: mature
Tags: My Little Pony: Friendship is Magic, Porn, Sex, Fetish, Limestone Pie, Slice of Life, Marble Pie
Length: 3194

Ponies think that Limestone Pie's problem is that she needs to get laid. They're wrong: she gets laid all the time. And when she fucks, it's just as rough as with everything else she does.

Ponies think that Limestone Pie's problem is that she needs to get laid. They're wrong: she gets laid all the time. And when she fucks, it's just as rough as with everything else she does.

That's her first surprise. The second surprise is who the fucking is rough for.

Contains: futa, incest

Written for the Incest Group's Siblings contest

Published 2019-04-30 11:10:01 UTC
Last updated 2019-04-30 11:10:01 UTC

Chapter 1

"Hurry up, you lazy bitch," Limestone yelled to Marble.

She heard Marble straining with the cartload of rocks she was pulling. In truth she wasn't really being slow, Marble just needed encouragement sometimes. Lots of it and violent. Exactly the kind Limestone was good at providing. The world had enough nice ponies; it needed some mean ones too.

Even so, she backed off for a while after that. She had been egging her sister hard all morning, and even somepony as timid as Marble had her limits. Limestone fully intended to push her past them, but that was for the evening. The day was for work.

Rock farming was an involved business. It had been hard enough with Maud and Pinkie around, but now that they were gone it was completely unfair for ponies to expect the farm to keep going with only four ponies. It was a familiar topic that Limestone could have bitched about in her sleep—and often did.

So somepony needed to be the mean one who kept everything moving along. Limestone didn't care how anypony else felt about her, and she wasn't about to start, so that job was hers. If they worked well and fast, she didn't give a shit if they hated her.

Igneous and Cloudy were getting old, so they stayed up in the fields moving the rocks around. That left her and Marble to work the quarry. They had the privilege of digging and breaking up the raw boulders and hauling them up to the fields.

They started in the morning, and worked all day long. There was no talking. Orders and insults did not count as talking.

Limestone was very impatient, and could not wait for evening. Not because the work was unpleasant—it was, but it was also one of the few things worth doing around there—but simply because she was a mare who had needs.

She did not go into town often, but it was enough to know what the other ponies around thought of her, said about her. They didn't like her and she didn't like them. She had tried, at Pinkie's insistence to get to know some of them, she had been dragged to a few evenings at the bar. It had been full of sad old ponies drinking their lives away—which was pathetic, she, for one, intended to work herself to death, the way ponies were meant to. Even worse, there were young ponies like her.

Nopony said anything when they thought she could hear, but she knew that a lot of them thought her problem was that she needed to get laid. Pinkie was one of them. Pinkie had talked her into making a deal with some of the young stallions: they would fuck her, but if she wasn't satisfied, she would beat them up after.

She had thrashed every stallion that took her up. One of them had even had the audacity to ask how it was after jizzing inside her after two strokes. She still hated him a little more than everypony else. He had cried like a bitch even though his leg healed fine.

The only reason she had gone along with Pinkies plan at all was because the ponies gossiping about her were right—it didn't matter how she felt about them, it was simply a fact they had stumbled on, and there was no point denying it. They were absolutely correct that she needed to get laid, and badly. They stopped being right after that. For one, how in Tartarus was she supposed to get any satisfaction when none of the stallions around could fuck worth a damn? Second, they all seemed to think that her attitude was just the result of sexual frustration.

She was sexually frustrated, but it wasn't why she was a bitch. She was a bitch because life was a bitch and that's just how it was. Horniness was a problem you could deal with—it was a problem Limestone could solve, unlike all her other problems. Except! Except she needed another pony for that. She had tried her hooves, she could shove rocks up her cunt all day, and it would feel nice. But she knew, deep down, that what she needed for real release was to get rutted.

There were no stallions around that were capable of doing it.

Which left her staring at her sister's ass as she strained to hold the rock cart up. Marble had tripped and nearly sent the thing tumbling all the way back down the quarry.

"You clumsy slut! Could you be any more careless? That thing damn near ran me over." She was careful, despite her anger, to keep the word 'slut' quiet enough so their parents wouldn't hear. She had a talent for insults, and that meant she did not use curses indiscriminately. The word would not have its intended effect if they heard it. She only called Marble a slut when she was both annoyed and particularly horny.

It figured that the only one of her sisters left with her was the sexiest. Marble had been forced to develop strong muscles like everypony else, but her ass somehow remained soft. It was the kind of ass that even Limestone could enjoy looking at. She enjoyed touching it as well. There was also the matter of Marble's freakishness. It worked on her.

She had sex with her sister, there, she admitted it. She had enough of a sense of decency to keep it quiet, but she and Marble frequently banged when nopony else was around and they weren't busy working. Which were rare things on a tiny farm in the middle of nowhere.

Suppertime came. After they had all eaten came the elaborate dance of excuses and fibs that it took to get both Limestone and Marble out of the house, and keep their parents in, and not arouse any suspicions.

Marble liked walks. Every evening she would go out wandering the property for a long time. There was nopony else around, so she enjoyed it.

Limestone had sensed that something was touching Holder's Boulder the night before, so she couldn't say that again.

She paced the living room. Her mother worked on some needlepoint, her father sat, silently watching his wife. As they did every night. She looked out the window. She could see Marbles silhouette moving along the top of the quarry.

Their family were the only four ponies within a dozen miles, and not a single one of them was in a hurry. Limestone thought. She reviewed the day looking for some unfinished piece of work to check. There was nothing unfinished, but nopony would ever say she was not thorough. It was obvious when she found her excuse. Stupid mare! she thought to herself. Not realizing sooner was just sloppy, completely unacceptable. But either way…

"I'm going to go check the cart," she announced. "The wheel hit a rock this afternoon. I need to make sure nothing is damaged."

As expected, there was no reaction as she walked into the night. Marble was nowhere to be seen out there.

She really did check the cart, just to be sure there was nothing she had missed. But it was the third time, so only a cursory inspection.

Then she went down to the quarry.

Limestone went to their meeting place. A nice little that nopony else knew about. There were a lot of little caves around, nooks and crannies in the mine. Only one was Marble's Rape Cave. Limestone had yet to find a better way to blow off steam from a long day than by being raped by her sister.

Marble was incapable of really raping anypony, of course. She was a soft pony through and through. And Celestia herself wouldn't be able to help anypony that actually tried to rape Limestone. Any creep tried that would just get murdered. But coming within an inch of it? Oh she liked that.

Marble was waiting for her, as usual. Limestone came in with a big mean grin. "Aren't you a pretty whore tonight? You look all ready to go around town sucking dicks for bits. Sure, you could be doing something useful with your life, but I guess it's better than nothing."

She circled Marble, stalking her like a predator. "For Celestia's sake, why do I have to be the only normal one?" She sneered every word. "The only one with any brains. And you're the worst. Pinkie and Maud may be 'special', but at least they can be useful. Somehow you ended up nothing but a brainless whore."

She shouted. "You're a whore! A slut! A freak!"

Marble was used to Limestone's insults But she had a limit. Even as used to it as she was, even with her shyness, she could only take so much abuse.

Limestone knew it. She kept hurling ever cruder taunts more and more angrily. Finally she got what she hoped for out Marble: a hoof smacking her across the face.The blow caught her mid-step; she lost her balance and went sprawling on the ground.

Marble walked up to her. She was almost stomping. Her hooves clacked loudly. She stopped, just in front of Limestone.

Limestone looked up into her cold eyes. This was what happened when she pushed her sister too far. Marble would let ponies walk all over her all day, but if you knew how to push her right, a switch flipped and she would be the one walking all over you. Marble could be as mean as her when it came down to it.

Not many ponies knew how to set her off. It was simple really. Marble Pie had a secret. A secret she was very sensitive about. She did not like being teased about it, which Limestone had just done.

She broke away from Marble's frown and stare, and let her gaze fall down to Marble's secret. She had two secrets, actually. The first was that she got horny when she was mad. The second, was that she had a penis. A big one. Limestone watched it slowly sway under her sister's barrel.

That was how their little game worked. Limestone got Marble all worked up and angry, and Marble stuck her dick in Limestone. Where it went in her, how hard it went in her, how long it went in her, Limestone had no say in. She was Marble's fucktoy for the night and there was nothing she could do to stop it.

Marble looked at Limestone staring at her rod. "And you call me the slut," she said, "when you enjoy this. See, this is why nopony likes you or ever will."

She'd heard that plenty of times. But it stung a little, coming from Marble. Marble knew how to hurt her too. It was the price she paid for good sex.

Marble stepped on her back. "At least you're not trying to talk this time. You know the drill: open wide and start sucking."

Limestone did as she was told. She wrapped her lips around the cock dangling in front of her. Once the head was fully in her mouth, Marble took another step forward, forcing herself back into Limestone's throat. Limestone gagged. She couldn't breathe. She forced herself to stay still as long as she could, but finally the burning in her lungs became too intense even for her.

She squirmed and rolled, and heaved the cock from her mouth. She gasped for breath. Her sister only let her get a little air down before she started again.

Marble ordered her to lie on her back. She complied, even though it didn't matter if she did—Marble would have just forced her otherwise. This time Marble squatted over her, giving her a face-full of balls.

Marble was actually quite a clever mare. she left the house under the pretense of going for a walk. It also gave her an excuse not to wash up right away after the work was done. So Marble was still covered in all the sweat of a long, hot day of hard labor.

Limestone's face was filled with a very pungent pair of balls. The odor of her sister's musk was nearly suffocating. And very arousing. Limestone could feel her cunt dripping. She needed more. She opened her mouth and started licking the sack above her. One of the few things she did like in life was sweaty ballsacks—and she'd kill anypony who found out.

Marble had to go to a lot of trouble to hide her assets. Most of the time, she wore a pair of tight grey panties that matched her coat. Ponies believed that it was just modesty, that she was so shy she couldn't even handle somepony getting a glimpse under her tail like a normal mare. Nopony outside the Pies knew what she was really hiding in there. She was very well endowed, the little shy mare. Her balls were huge, bigger than most stallion's, and hung loose. They filled Limestone's mouth completely, when she transitioned from licking them to sucking on them.

She would have done that for however long they were in front of her like that, like the good little slut she was, but she didn't make the schedule, Marble did. Marble stood, yanking her testicles out of Limestone's mouth with a pop. She didn't look down at her sister, or move in any way, why should she?

"Get up, you bitch, and stand in front of me so I can mount you," Marble said in the same cold tone as before.

Limestone scrambled to her hooves and presented herself. She was so wet. She needed that cock.

Marble gave it to her. There was no warning, she just reared up and slammed herself into Limestone.

Limestone gasped as her cunt was suddenly stretched. She was so wet that it easily slid into her. Then her breath caught and she shuddered with pain as Marble's stroke bottomed out and tapped her cervix.

A hoof on the back of her head forced her face against the ground. There was a pebble that pressed into her cheek. She hardly noticed that, as Marble started to fuck her hard and fast.

This is what none of the stallions had been able to give her. She needed to be pounded. They'd all been too scared, too weak, or both to do that to her.

She didn't need to be loved. She didn't even need to be fucked. What she needed was to be used. That's what Marble was doing. She was making her cock feel good without any thought for Limestone.

Marble was not gentle. With every stroked she pulled out fully, leaving Limestone's pussy empty and hungry. Then she slammed her whole length in (most of it, she was merciful enough to ease off on her sister's cervix after the first time). Limestone gasped every time the thick log of horseflesh plunged inside her. The gasps mixed with the loud, wet squelches her cunt made.

She shook, barely keeping her hind legs from collapsing. Every time the dick was in her she squeezed her pussy, trying to hold it in place, but never hard enough. It only added a twinge of pain as Marble forced her way through the clenched muscles in addition to the natural tightness of her pussy.

Every now and then, Marble would spank her, just for good measure. Each smack of hard, rock-breaking hooves on her flank forced a yelp out of Limestone.

It hurt, and she fucking loved it. It made her cunt even more desperate. The stuffing she was getting was barely enough. She relished each blow as they pushed her closer and closer to orgasm. An especially hard hit pushed her over the edge, and she came for the first time that night. Marble was straddling her tightly, so she couldn't melt and lie on the ground like she wanted. She wasn't thinking much before, but her mind went blank then, from the sheer overload of sensation.

Marble had far more stamina than any stallion Limestone had fucked. She kept up the assault for what felt like hours, never tiring or slowing. Limestone came two more times. Finally, Limestone heard her start to grunt occasionally. She had recovered enough of her senses to know what that meant. The pace increased.

Marble yelled. Limestone felt her cock swell and flare deep in her marehood. Then came the hot rush of cum. The thick, creamy seed filled her, came spilling out when Marble withdrew. Limestone's chest heaved. She took deep breath's now that she was free from her sister's iron embrace—and also because of the load inside her. She didn't know what she'd do when Marble inevitably knocked her up. That's part of what made it all so exciting.

She could finally collapse to the cave floor. Marble was still frowning when she looked at her: it wasn't over yet.

"I was feeling nice," Marble said, "so I let you get me all wet and slippery before I fuck your ass." She pulled Limestone back to her hooves by the scruff of her neck. She placed the tip of her cock, now covered in both mare's cum, against Limestone's ponut. She pushed.

Limestone still had to bite her lip hard to endure the sensation of having her ass stretched. Marble was so big that her ass could never get used to it. Somehow her ring managed to admit the huge girth, and the whole thing started sliding in. Soon her colon was filled with cock.

Marble didn't fuck her ass any more gently. But taking a dick there felt so much dirtier. Marble had been right, at the start. If either of them was a slut, it was Limestone. Limestone was the nastiest of the Pie sisters. Limestone was the one who was only good for being a cocksleeve. Limestone was cumming.

It took a lot of work to give Limestone an anal orgasm, so Marble wasn't far behind. Unlike with the pussy, though, she could go deep. Limestone screamed as she hilted herself in her butt. She unleashed another blast of cum, as far inside as possible.

As slowly as she had entered, she pulled out. She sighed heavily, finally satisfied. The way Limestone was crumpled on the ground, a vacant look on her face, showed that she was satisfied too.

She pulled her to her hooves a third time. This time letting Limestone lean against her for support. Her sister's leg over her shoulder, she lead them out of the cave, and up out of the quarry.

"Are you okay?" she asked, back to her usual soft whisper.

Limestone stretched, full of aches. "I'll be fine in the morning. You don't need to worry so much," she grumbled.

Everything was back to normal. They went inside and cleaned themselves up. Then they went to bed.

Limestone and Marble had a secret they didn't dare tell anypony else about. Sometimes, now that Maud and Pinkie were gone and they had their room to themselves, they would sleep in the same bed, and cuddle all night long.