The problem with being turned on, Twilight decided, was that it rather acted like a fire in the mind. Even if it had mostly been put out, all that was needed to re-ignite a blaze was one single hot spot. And it was this issue that Twilight found herself facing barely a minute after departing from Fluttershy’s cottage. The idea that Rainbow and Fluttershy were having hot diapered sex this very moment while she was off to work in Canterlot was not only frustrating because she knew that if she had stayed she would never work up the desire to fly the distance to the castle for only a half day of planning and meetings, but it was doubly so since no matter how she thought of either Rainbow or Fluttershy, even when considering such pedestrian matters such as what Flutters would consider to be the best squirrel food, she was reminded that diapered sex was a thing. It was this concept that she found keeping the spark of arousal hot in her mind.

As Twilight flew over Ponyville she came to a decision, either take drastic action now, or spend the rest of the day only being able to partially concentrate on what was going on around her due to a certain desire.

As she had by now passed beyond the edge of town she banked hard around and descended. Aiming herself towards a fancy looking two-story circular structure perched on the edge of Ponyville. If Rarity was in, and Twilight suspected she was as the pony had just spent several days in the capitol and was probably resting a bit, then there might be some relief for her yet.

Landing with a soft ‘thump’ Twilight touched down in the knee- high grass besides a stone path located behind the Carousel Boutique and walked up to the back entrance, a door through which only delivery ponies and certain kinds of customers would head towards.

Ascending the steps brought her near enough for a few gentle taps on the door with the tip of a hoof.

Twilight’s sensitive hearing allowed her to catch a few mumbled comments about inconsiderate ponies and what time it was, which reminded Twilight, perhaps a bit late for preventing embarrassment, that it was indeed still rather early in the morning.

A small slat slid open in the door and a single eye peered out at Twilight.

“It’s simp- Oh… Um, good morning Twilight, um… I do… well I do suppose you may come in…”

Rarity unlatched the door and opened it just wide enough to allow Twilight to slip inside and into the back workshop. Whereupon Rarity swiftly closed and re-latched the door.

As soon as Twilight turned around she immediately identified the reasons that her friend had for her hesitation in allowing Twilight inside.

First of all, Rarity had apparently done nothing to keep her mane or tail in their usual perfect arrangement so that hair was sticking out at interesting angles and much of her coat looked like it had been petted backwards by a giant hand. The second reason, and assuredly the more obvious to anypony who did not know Rarity very well was the presence of a very thick disposable diaper hugging the mare’s butt and thighs. It was mostly white but was printed in several strategic locations with silver versions of the wearer’s cutie mark and instead of white was light pink around the leg openings and around the top of the diaper’s waist. However, the majority of the white plastic of the diaper was subtly tinted a light tan color. A shade Twilight recognized as the result of a lot of pee mixing with a big load of poop that had soaked completely though the padding.

The smell permeating the workshop confirmed what Twilight’s eyes were telling her.

Twilight had to pause for a moment to consider that as this was Rarity, if in fact she was more reluctant to let anypony see her in this state more because of her messed up hair and fur than because of the diaper.

She decided that it might be a draw.

“I’m so sorry Rarity, I didn't consider how early it still is, and you just got back last night didn't you?” Twilight said before Rarity could say anything.

“Oh, um, yes…I did, but not to worry. I was already up and about, have been for a while, actually. It’s just that I wasn’t expecting any company… as you can see I suppose. So, what brings you by then?”

“Oh that.” Twilight started, now feeling a bit ashamed of herself, appearing unannounced at her friend’s back porch only an hour after sunrise looking for quick sex. It really was rather shallow of her now that she thought about it.

But on the other hoof, she couldn’t just simply leave now that she had intruded this far.

Though still feeling bad about it, Twilight couldn’t help explain herself truthfully.

It’s just that, well, I’ve got to go to Canterlot today and I happen to know that Rainbow and Fluttershy are getting to spend a lot of um, quality time together today, and I was in too much of hurry to properly take care of my needs before I left from Fluttershy’s cottage and I can’t go back there now because if I do I’ll get involved in what they are doing too much and by the time we get that all over with half my day will be gone and I can’t have that happening so I need to do something about my situation and quickly and…”

Twilight trailed off, realizing she was rambling on at an ever-increasing rate of speed. And because she realized that the whole time she had been speaking she had been gazing fixedly at the big, thick, and very comfortable looking diaper Rarity had taped about herself.

It was only after tearing her gaze from the diaper and back towards Rarity’s face that she saw her friend was smiling quite broadly. This was a much better result than the scowl she had been half expecting.

“So Twilight dear, let me get this straight, you got yourself more horny than you realized this morning thanks to our two dear friends and now you need a quickie because if you don't do something you’ll be desperate for sex all day? And you came looking for me to help?”

“Hehe… yah…that, that's about it, yah. Twilight said awkwardly, absently rubbing one foreleg with the other.

“Well, I suppose you've come to the right place then haven’t you.” Rarity said, still refusing to look annoyed.

It took a second for Rarity’s reply to sink in, but when it did Twilight couldn’t help blushing deeply. She found herself thankful that most of her face was covered by fur to hide the color change.

So, if that's what you’re hear for, get thoes saddle bags off and raise your tail.

“I…yes, ok.” Twilight said.

Caught off guard but the abruptness of Rarity’s request Twilight wondered if perhaps the pony did in fact just want to get back to sleep.

But then the grin that Rarity was doing a poor job of concealing suggested otherwise.

Twilight did as instructed and laid the saddlebags down by the wall and turned her butt towards the other mare and waited. Though she couldn’t help keeping an eye on Rarity to see what she did.

Rarity held her diaper up with her horn as she began to untape it, obviously not wanting to let it just plop down onto the floor. Having undone only two of the four tapes rarity turned a sidewise glance at Twilight.

“You do realize my diaper is rather soiled in front right? So it's a bit you know…”

Twilight knew exactly what ‘it’ Rarity was referring to.

“That’s exactly what I was hoping for you know.” Twilight said now smiling herself.

“I thought so.” Replied Rarity.

Having made sure the both of them were on the same page, Rarity continued with the removal of her diaper. Twilight shuddered a bit in anticipation as Rarity lowered her bulky diaper to the floor and neatly folded it over on itself and laid it on a chair.

Rarity’s thick black shaft was now fully exposed and rock hard. The same light brown goo that filled the rest of the diaper was smeared along its length, occasionally dripping from her large heavy balls.

The smell that came from between Rarity’s legs made Twilight want to gag, but was oddly intoxicating all at the same time as though one part of her mind associated the stench with great pleasure but the other part was disturbed by this very association. Fortunately for the sake of sexual gratification, the association with pleasure won out and she lifted her tail and felt her wings spread out in growing anticipation.

“I’d just like to know Rarity, before we begin, how long you’ve been like that in your diaper?”

“Oh, well let’s see now, I went quite a lot almost as soon as I got back last night. I of course made sure to squish it up into the front of the diaper, you know.”

“Of course.” Replied Twilight, grinning.

“Anyway, I went to sleep soon after, too tired for anything else you see. Then this morning, less than an hour ago I messed and wet again.

“Your penis has had a nice long time squishing around in your poop then hasn’t it.” Twilight observed dryly.

“Its enjoyed a very long and pleasant poop bath, yes. Which is why I’m now quite pleased you so conveniently dropped by. I was getting increasingly horny in my diaper, and something was going to have to be done eventually.”

‘Was that a pun?’ Twilight wondered silently.

“Then what would you have done if I hadn’t come along?”

‘Well if it wasn’t then it is now.’ Twilight decided.

“Oh, Sweetie Belle’s asleep upstairs. I suppose I would have gotten around to asking her for a favor or two eventually… but this way she can sleep in a while longer.”

“I see.” Replied Twilight.

The fact that Rarity’s only truly constant girlfriend was her own younger sister always managed to make Twilight feel a little less unusual in her own sexual preferences. Which was a feeling that she wasn’t sure she should communicate to Rarity. Though in the unicorn’s defense, if Shining had been a mare… Well, Twilight had Cadance which made for a good enough consolation prize.

“So, you ready Twilight”

“Absolutely! Oh, and Rarity?”

“Yes Twilight?”

“Please don't be gentle.”

“Yes Princess.” Rarity replied as she pressed the poop smeared head of her thick black shaft against Twilight’s wet pussy.

With a satisfied grunt Rarity mounted Twilight and plunged her messy shaft deep into Twilight’s tight vagina all in one smooth swift motion.

The sensation of suddenly being so full between her legs and of the slick poop providing additional warm lubrication proved enough to cause her front legs to fail in supporting her body. As her front slumped to the floor her backside stayed high in the air providing Rarity plenty of opportunity to thrust herself as deep inside Twilight as she could get.

She clenched herself around the long thick penis filling her and felt too the sticky, squishy feeling each time Rarity’s poop covered balls were pressed up just under Twilight’s dripping clit.

With what was left of her ability to think Twilight decided that having hot messy poopy sex with a mare as capable as Rarity on a morning like this was one of the best ideas she had had in ages.

Rarity thrust and thrust again, each time letting out a new type of moan or grunt along with plenty of squishes and squelches as the two pony’s organs pleasured each other.

“Hey Twilight…I wonder, by the time I’m done, will I have filled you with more of my cum…or my shit?”

“I don’t really care, Rarity, as long as it’s a lot of both!”

“Ohhh, just what I wanted to hear…”

Conversation ended as Rarity’s thrusting became more insistent and less regular as she pressed in harder and held herself inside for longer.

Twilight knew Rarity was about to cum when she leaned over Twilight and held her body tightly between her forelegs.

As thick cum gushed deep inside of Twilight, Rarity made more a series of loud panting gasps than a real scream and she shuddered and trembled as the warm thick ejaculations mixed with the nearly liquid poop that had been accumulating inside Twilight with each intrusion of Rarity’s member. Such was the composition of the slimy fluid that now bathed Rarity as she held herself inside her alicorn partner.

Twilight for her part was unpleasantly surprised, she was close, yes, but Rarity had come too quickly, a very armature move from a mare so supposedly experienced.

“Uh, Rarity, I haven’t-“

“I’m not done yet Twilight, just hold on.” Rarity interjected.

Almost as soon as Twilight wondered what Rarity’s plan was, she felt it.

A hot powerful flow of pee erupted out of Rarity’s still very hard penis and exploded deep inside Twilight’s vagina. Almost at once, Rarity resumed her powerful thrusting while continuing to urinate strongly. The previous squishing sounds were now replaced by splashing as with each deep and powerful thrust of Rarity’s hips a spray of glistening yellow pee was forced out under pressure around the unicorn’s shaft to splatter over her balls and back legs.

This new and rather unique sensation and the feeling of having her body being so wonderfully violated by the waste of another mare was enough to make Twilight cum with a cry and a spray of clear fluid that mixed with Rarity’s yellow.

Rarity made sure to hold on to Twilight’s hips to keep her penis in place as Twilight wiggled and pushed against her crotch while she came. Finally, with a moan Twilight slid herself off the penetrating organ and slumped to the floor breathing in gasps while an interesting mixture of fluids leaked out of her pussy.

Rarity, managing to remain standing, watched Twilight with a mixture of love and prideful satisfaction at her ‘conquest’ while fetching her very messy diaper off the chair she had laid it on. With carefully practiced magical manipulation Rarity eased the poop smeared and pee filled disposable diaper up between her legs and back over her cock and balls, then up over her butt. Once secured firmly back into place she pulled the tapes tight and pressed them down, re-sealing all her sensitive parts back within the warm and slimy confines of her bulging diaper.

Getting back to her feet proved a bit of an effort, it was awfully nice down there on the cold floor, but the whole point of going out of her way to see Rarity was to have great sex and have it fast. Lazing around would only serve to negate her advantage.

"Thank you so much Rarity, that was wonderful, just like I knew it would be.” Twilight said before giving Rarity a quick kiss on the lips.

“Mmm, pleasure’s all mine, not every filly’s lucky enough to get to do that with a princess.”

“Not every princess is lucky enough to have a mare with a diaper full of poop so ready and willing.”

“That’s not true, actually.” Rarity said dryly.

“Right well, I’m still lucky…” Twilight said awkwardly.

“I’m sorry Twilight, you’re just too much fun to catch off guard.” Rarity said leaning her head on Twilight’s shoulder.

Twilight couldn’t help but quite keenly feel Rarity’s diapered hip on her own bare one.

“I guess since you already have your diaper back on it would be too much trouble to remove it again and let me suck you off or something… But I do wish I could do a little to repay you before I go.” Twilight said.

“Well, to be honest I was going to say that being able to cum inside a princess with a poopy dick was its own reward, but now that you mention it…”

“Here, if doing things quickly is the theme of the morning, then let’s try this.”

Rarity once again undid the tapes of her diaper, but she did so while remaining standing so that the front of the diaper, underneath her in this position, opened and hung down between her back legs. Twilight watched the glistening layer of poop spread around the inside of the diaper to see if it was going to immediately start dripping off onto the floor. The consistency was such, similar to slightly too wet peanut butter, that this did not happen, though Twilight figured that a few minutes in this position might prove sufficient.

Rarity seemed to have come to the same conclusion.

“Well, better get a move on shouldn't you.” Rarity said, prodding her thick black cock at Twilight’s lips.

Having been placed back in the diaper for a few minutes it was once again just as poop smeared as before Rarity had done her best to clean it off inside of Twilight.

Twilight decided that hesitation would get her nowhere under these circumstances and so she opened her mouth wide and slid her head forward at such an angle that Rarity’s wide glistening length was lined up with her throat.

She felt her gag reflex grow quickly stronger, but her experience and mental control over her body allowed her to overcome it just as fast.

Rarity grunted with pleasure and began to throat-fuck Twilight, pumping her slimy shaft in and out as far as she could go, causing her open diaper to swing back and forth between her spread rear legs.

The poop that had been on Rarity’s penis was now doing an equally good job of coating the inside of Twilight’s mouth. If Twilight was honest she’d say the taste was not great, mostly bland and a bit bitter. But taste was hardly the point. It was the feeling and the texture of everything in her mouth that she loved, and she swallowed as often as she could.

All the subtle indicators, the more frantic breathing and pumping, the grunts and moans, and the taste of pre-cum all told Twilight that an eruption was eminent.

As predicted, Rarity curled a foreleg behind Twilight’s head and pressed her forward so that her muzzle was pressed into Rarity’s shit-smeared balls as the unicorn came for a second time like a fire hose, straight down Twilight’s throat, where she could feel the hot cum splatter around inside her neck.

Gaging slightly as Rarity removed herself, this time from Twilight’s other end, Twilight tried her best to steady her breathing as she swallowed anything left over in her mouth.

“Thank you Twilight dear, I really did need that. Cumming once around you is never enough, I should have learned that by now.” Rarity said as once again, she taped the thick disposable diaper back over her erection, allowing the diaper to hold the shaft firmly in place so it could soak for hours yet to come in the warm squishy darkness inside Rarity’s discolored and bulging diaper.