Rarity designed many things for her boutique, whether that be the decorations that lined the store's walls or the various products she sold on a daily basis. One could mistake her store for only selling dresses, but she didn't get to be one of Equestria's most premier fashion brands without branching out. Dresses, tuxedos, jewelry and other accessories, and some everyday wear for good measure. She even had some custom orders outside of her usual production, but that only meant a challenge for her to take on, and she was always up to the task.

Then Coco placed her order.

It wasn't unusual for her protege to ask for her assistance with a personal project, but it did strike Rarity as strange when she came into the store furiously blushing as she passed over a small envelope muttering something about a 'very special request' she wanted Rarity to put together. Coco hardly ever relied solely on her mentor for any creation, so she must be really stumped on this one. Unfortunately Rarity hardly had a moment to ask for more details before the shy mare was already out her door.

Rarity sighed to herself as she carefully opened the envelope Coco had left behind, pulling the short parchment out and silently reading the request to herself. The request itself was extremely vague, only stating that she had need of a unique garment that neither of them had created before for 'personal reasons'. Coco also said that she had created a concept for the garment, which was included on the back, but needed Rarity's expertise and larger pool of resources to see it become a reality. So far nothing truly out of the ordinary, though Rarity did question why Coco was so concerned about utility for a fashion project.

Rarity flipped the paper over, doing a sharp double take the moment her eyes landed on the sketched design. What was scrawled out before her was an outline for a custom-made diaper. That alone was enough to throw Rarity off, seeing as she had barely even touched standard undergarments in the years of running her business. Why would Coco be asking this of her?

Whatever her reason may be, the more Rarity read the more she realized that the demure mare had put a lot of thought into this decision as every aspect of the diaper's construction was accounted for. Not just the general aesthetic and design flairs, but even the shape and materials. It was probably one of the puffiest designs that Rarity had ever seen, and from what fabrics and plastics Coco had recommended, it was supposed to be very absorbent and almost entirely leak-proof. This was meant to be used, and used a lot.

Rarity sat in disbelief, trying to rationalize in her head what Coco could possibly need a diaper for, let alone one so meticulously crafted. At first she wondered if it was even for Coco herself, but the measurements perfectly matched the one that Rarity had on record for her partner. There was no question that this was for Coco to wear, so the next best reason Rarity could come up with was perhaps a medical one. Maybe she just suffered from incontinence? A little embarrassing, sure, but it was better rationale for Rarity than any... other reasons Coco might want such a thing.

With a safe motivation in mind, Rarity set to work. The letter requested a small batch of about six to be made as a trial, and if they turned out the way Coco wanted she'd ask for more. Gathering the materials was fairly straightforward, though Rarity did hesitate a little as she was putting the first diaper together as she reflected on just what she was doing for her friend before reminding herself this was probably a necessity and Coco wouldn't be asking this of her otherwise... right?

Rarity also couldn't help but think of how she usually handles her customers and how she might have to play things different with this. Normally, she'd be ecstatic to see her client try on their finished request and watch their excitement as they express just how perfect a job she had done for them. She loved seeing that from Coco especially, but she wasn't sure Coco would even try this on in front of her, expressing nothing more than sheer embarrassment and trying to leave as swiftly as possible.

For some reason, though, the mental image of Coco wearing this didn't immediately leave her head, nor did she even consider for a second how awkward it would be for her to see Coco wearing it; perhaps her desire for her customer's satisfaction was trumping the strange circumstance she might face? Whatever the reason, that image stirred her to press on, and she finished the first of the set by day's end. As she went to put it away and set up to start on the next one, a thought crossed her mind that she really never had to consider with most of her other works. Everything else she made was just aesthetic, it wasn't meant to do more than compliment a pony's looks or the rest of their ensemble. These had a particular use, and if she was going to uphold her own quality values, they had to work as Coco wanted them to.

Which meant Rarity needed some way to test them.

This posed two problems to the fashionista, the most obvious being how she could possibly go about testing one of them to be sure that they would be what Coco wanted. She wasn't about to tell anypony else about this side project, which meant that she could either invite Coco back and find out what she thinks of this first draft, or... she could test them herself. On the one hand, Rarity would usually keep in contact with her client to discuss potential alterations, but considering the way Coco had originally given Rarity her request it was unlikely she'd come back before they were actually done. Not to mention living all the way out in Manehattan made commutes far more difficult to arrange than a simple jaunt around town.

On the other hand, Rarity was not keen on subjecting herself to the humiliation of purposely wearing a diaper, let alone using it. She could always just continue making them as Coco had designed and hope that it would work for her, but that went against her own quality assurance standards. Thus, it was a war against her business morals and her personal dignity, and in the end, her morals won out. While she was also disappointed to waste the entire night's work, it was better to waste one rather than six and have to start from scratch because they didn't turn out right.

Still, Rarity wasn't going to make it super obvious what she was doing, so she retired to her bedroom for the night with the diaper kept in a small work satchel, shutting and locking her door before she undressed and hesitantly wrapped the garment around her waist and crotch. It took a little bit of extra effort as Rarity's hips were quite a bit wider than Coco's, but she eventually managed to get it secured to her body.

She had to admit, Coco had done a very good job designing the diaper to be as comfortable as possible. Despite the tighter fit, the waistband wasn't digging against her hips, and the rest of the cloth and padding felt surprisingly soft against her fur. The only thing that Rarity questioned was the size, as despite being smaller on her the main padding of the diaper was still puffy enough to force her legs slightly apart; she could only imagine that Coco would always have to have her knees bent just to accommodate, and that would be before she even used it and made it even puffier. Once again, the thought of Coco wearing and using the diaper didn't seem to bother her that much. For a moment, she thought it would be kind of cute.

A small ache in her bladder snapped her out of her thoughts, and she quickly recognized that she wasn't holding it for very long standing like this. With that, she climbed into her bed and hoped that she would be able to fall asleep before her body decided to let go, but she quickly realized that everything she was just praising about Coco's diaper design was clearly intended to coax the wearer into using it. The wide padding made it harder to hold her pee in, and the softness of the interior helped relax her entire crotch. Rarity tried holding out for as long as she could, a few spurts escaping before her muscles gave way and she began peeing herself in full force.

Rarity didn't even realize just how much she had been holding in until she felt it splash back against her pussy before soaking into the diaper's thick padding. A soft gasp escaped her mouth as the warmth spread across her nether regions, the diaper slowly pillowing out between her legs. The world around her briefly slipped away as her mind focused solely on the blissful sensation she was experiencing.

Her senses slowly returned to her as her stream of urine died down, leaving only a few drops to seep into the fabric pressing further against her pussy. Rarity gently cupped her hand around the front of the plastic garment; she could feel the extra weight from all the pee it absorbed, but even squeezing it didn't allow any to leak back out. Satisfied that she had done her job well, she turned over to sleep for the night, content to leave the diaper fastened to her waist as she drifted into slumber.

The more days went by, the prouder Rarity was of her own work. That first diaper she had tested out was absorbent enough to last her several nights, though she still wondered how well they would work for Coco. She still wasn't sure why her protege had made this request of her, but based off of the design and effort Coco had put into it, she had come to one of two conclusions; either Coco had some medical condition that made them a necessity, or she just really enjoyed spending her day in a diaper that she could use over and over again.

Rarity had slowly come to hope for the latter. She wasn't sure what about the idea of Coco in these diapers was so appealing to her, but the more she worked on them the more she was certain that she wanted to see Coco in one before she took them back to Manehattan. Thankfully she didn't have much longer to wait; she had just finished the last of Coco's trial batch, and they had already arranged for Coco to pick them up the following day. Some part of Rarity was tempted to wear one when Coco arrived, but she felt that would embarrass the mare too much and she wouldn't stick around for what Rarity really wanted. No, she'd hold off on showing her hand until the time was truly right.

Coco arrived in the same manner she had when she first dropped off her request, scouting her surroundings for any other ponies as she approached the main desk. Rarity watched the flustered mare with slight amusement; she always found it cute when Coco was nervous. "You don't have to be so anxious, dear. I closed down the shop a little early for your arrival, so it's just you and me here."

"Oh, thank you Miss Rarity," Coco replied, though Rarity's precaution seemed to have done very little to calm her down. "I'm sorry, this past week has been a little stressful."

"Oh? Perhaps you'd do me the favor of indulging me while we head in back?" Rarity proposed. "I so rarely hear of your stories from Manehattan, and it would be nice to do some catching up before you run off again." Rarity knew that wasn't what Coco was exactly referring to. Waiting in relative silence for a project that Coco wasn't even sure she'd take up was probably quite taxing for her, then to find out that Rarity did take it on and had it completed within a few days? Poor girl was probably bouncing back and forth between excitement and sheer terror at returning to pick up her request. Assuming she asked for them specifically for her pleasure, and Rarity continued to assume as much; it got her excited in a way she never imagined, and she was inches away from seeing the fruits of her labor.

It didn't matter if she was paying attention to anything Coco was saying, as her protege was just trying to come up with random stories to justify her 'stress' over the past week. So she let her imagination wander, picturing her company walking beside her with one of the diapers hugging her waist and wondering just how she might end up using them. She still wasn't sure if Coco needed them so thick and absorbent because she wanted to use one for as long as possible, or if she just let out that much in one sitting. She kinda hoped for the latter; watching Coco pee herself so much that she couldn't even stand with her thick diaper would be such a treat.

Rarity tuned back in to Coco's words as she took a break from her made-up work woes to say "You know, you could've just packed these up and sent me on my way. I don't think its really necessary to spend any more time on this than we need to."

She wasn't getting out of this that easily. "Oh nonsense dear, I have to be sure you are one hundred and ten percent satisfied with what I've crafted for you, and I can't exactly do that if you're all the way back in your Manehattan apartment!
I assure you, this will be over before you know it- Ah! Here we are!"

Rarity shuffled through some of her loose swaths of fabric to dig the diapers out of their hiding spot; she may have come around to them, but she still wasn't letting any of her other friends see that she had them. She carefully pulled the box from the corner, turning to face the younger mare and setting the box down on a small table between them. "Well? Go ahead and tell me what you think!"

"Oh, well, I, um, you know, they- they look perfect Rarity OkaynowigottagoBYE-!" Coco tried to back her way out of the door only to be enveloped in a sapphire miasma that gently pulled her back in.

"Coco, dear. You have nothing to be embarrassed about. You asked me to make these for you, and I have. All that I ask in return is that you give me your honest feelings on them, just like any of my other designs," Rarity assured her. Coco took a deep breath before sitting back down, hesitantly pulling one of the diapers from the box as she looked it over.

"It's- you did a good job, Miss Rarity. Just as good as you always do." Her praise was stiff, almost robotic, but the small curl to her lips gave away a deep excitement just from holding it in her hands. Rarity recognized the expression Coco wore, possibilities running laps around her head; it was the same expression she herself had seen in the mirror over the past few days. Time to see how far she could push her limits.

"I'm glad you think so, dear, but there is one last bit of quality assurance that I hope you'd allow me." Rarity requested, taking on a softer tone. "You know how much I love to see my clients try on their new outfits."

The number of emotions Rarity could read on Coco's ever reddening face was almost staggering: confusion, excitement, some returning anxiety, fear, and even some relief. All because she was treating this as though it was any other day in her shop. "You know where the changing room is. Go ahead, I'll wait right here."

Coco wordlessly stood with the diaper held to her chest, carefully stepping past Rarity towards the changing booth before disappearing behind the curtain. The anticipation electrified Rarity's nerves as she slid her hand down her body to gently rub between her legs. Moments away from the sight she had been dying to witness since she began this job, and it was making her so damn horny.

"Um, Miss Rarity?" Coco called out, prompting Rarity to peel her hand away from her crotch as her friend's face poked out from around the curtain. "I'm not so sure I can come out like this..."

"Oh, don't you worry about a thing, dear! It's just you and me here after all, and I'm not here to judge your tastes." Not negatively anyway...

Coco took a solid gulp of air before slowly stepping away from the curtain, having only discarded her skirt and panties in favor of the diaper. Just as Rarity had expected, the diaper's padding spread Coco's gait so far that she had to keep her knees perpetually bent. Her posture gave the impression that she was ready to piss herself at any moment, and from the look of sheer concentration on her face that might actually be true. It took all of Rarity's own willpower to keep herself from just masturbating to the sight in front of her, but she knew that could wait for more.

"Oh Coco, you look simply delightful!" Rarity praised as she stood and got a good look all around Coco; she was clearly at her limit, and it would only take a little bit of coaxing to get her to let go. Still, Rarity wanted to enjoy this for just a little bit longer. "Does it fit well? Is it comfortable? I did my best to craft it according to the sketch you gave me, and I hope its everything you were expecting."

"They're... they, uh... listen Rarity, I- I don't think I can stay like this..."

"Oh, what seems to be the trouble, dear?" Rarity teased as she paced around her friend. "I mean, you must have been so excited to finally come pick these up. To go home and wear them. To use them..." Rarity's voice dropped closer to a hushed whisper with every word. "Go ahead, Coco. Use it, just like you've always wanted to."

Rarity's sultry tone pushed Coco over the edge, a loud hissing from the diaper proving another of Rarity's assumptions; when Coco had to go, she went HARD. Within a few seconds her diaper had expanded to just above her knees, and the sound of her pee took on a fuller tone as the padding absorbed more and more of it. Coco's legs bent further to accommodate, to the point that she was just about sitting on the floor.

Rarity watched with glee, shoving her own hand back down her panties to get herself off as Coco continued to soil herself. From where she was watching, it almost looked like Coco was getting ready to do more than pee, and that thought excited her even more. She wondered if Coco would be willing to do that for her...

Coco's stream slowly died out, the young mare releasing a heavy breath she didn't even know she was holding. Before she could regain stock of her surroundings, a husky voice called over her shoulder, "Was that all you needed to do?" She recognized it as Rarity's, but she had never heard her mentor speak like this before. It was a voice that sparked a fire in her loins, one that immediately drew her to do whatever it asked of her. "You've wanted these for so long, right? Now you finally have them, and shouldn't you use them to their fullest? Don't hold anything back, you can finally indulge yourself like you've always imagined."

What little shame Coco had remaining washed away with every word as she spread her legs and relaxed her anus, pushing out the large shit she had been holding onto all day. It quickly stuffed her diaper, first tenting out the back before it coiled down below her. Her diaper continued to expand underneath her, the outer plastic pressing against the floor and forcing the rest of Coco's poop to cram into the back of her diaper.

Rarity shoved two of her fingers into her pussy and vigorously pumped them back and forth as she witnessed Coco live out her fantasy, desperately trying to bring herself to orgasm before the young mare was done. Both the sight and the sound of Coco's subtle grunts and moans made her so wet, and each pump of her fingers splashed her juices against the cloth of her panties. Within a few minutes her climax erupted, her pussy coating her hand and underwear in a thick coat of her cum.

Both girls sat in their afterglow for several minutes before they went separate ways to clean themselves up. When they had returned to the front of the shop, Coco was just as bashful as when she arrived, but she gave Rarity a solid thank you before leaving with her merchandise. Rarity giggled to herself as she watched the door close; Coco would be back very soon.

After all, that sample package wasn't going to last her any more than a week.

Author's Note

So I have a couple ideas for upcoming chapters, and I want to put it to a vote which should come first.

Trixie/Starlight - Trixie hasn't forgiven Starlight for trying to trade her wagon away, so on their way back to Ponyville, Trixie decides to teach Starlight a lesson. With some hypnosis, of course.
Sunset/SciTwi - Sunset introduces her Twilight to either an Equestrian custom or something from her college parties, haven't decided which yet (She could also lie about this reason and its just her own fetish anyway)
The Dazzlings - I'm thinking each meet up with a different member of the Main 7 and end up in diapers for different reasons (Aria/Pinkie dating w/ a mutual fetish, Sonata roleplaying w/ Fluttershy, stuff like that)
Holding Contest - This is something I definitely want to do a chapter on, and I'll leave it open to who's involved. Ideas so far are a collective Mane 6/Main 7/CMC chapter, or a new group like Twilight's Canterlot friends or the Shadowbolts

A chapter for Cadance is already in the works, and will either come out next or after the most voted suggestion here.