[i]The sun was setting over the rim of the Crystal Valley, and the soft and even lighting refracted through the valley's abundant namesake, casting the plains below in a glittery glow. In the center of the valley, the Tower of the Sun Princess stood tall, rising about the valley's rim. It was right outside the Tower where the two unicorn adventurers made camp. Tomorrow they would brave the dungeon, in search of treasure.

The male unicorn, a paladin, was washing his sword in the knee-deep stream that passed through the valley. Satisfied with the result, he rejoined his sister, the wizard. She was laying on her stomach in a patch of soft grass, studying her spell book. Her naked rear reflected the multicolored sunset; she'd grown into a gorgeous mare that took his breath away.

Meanwhile he hadn't changed a bit from his foalish days.

She noticed him approaching and patted the grass beside her. He went to her, as if in a trance. She put her hand on his belly, and he tensed. She leaned in and whispered into her older brother's ear:

"Does my big boy need to get his nappy changed?"[/i]

The immersion shattered.

A teenage Shining Armor was in his family's living room with his sister (and current Discipline Master) Twilight Sparkle. “Hold on, Twily,” he asked. “Why does my character have to wear nappies?”

The filly peeked over the top of her DM privacy screen. “Because it’s more realistic, obviously. Boys wear nappies.”

That was true. Shining looked under the table between his legs, where his thick diaper forced his legs apart. He’d peed in it an hour ago, and the padding was starting to get cold and clammy, clinging to his legs uncomfortably.

“But it’s a fantasy game!" he whined. I already know what it’s like to wear nappies, I do it all the time.”

Shining knew the real reason why Twilight was making his character wear diapers. Dragons and Discipline was an educational game, created by the Equestrian Department of Culture to encourage teenage creativity “within the acceptable bounds” set by the government. That was why it had a whole section of the rules for handling diapers, and diaper checks, and diaper changes, and encouraged colt players to use them. And Twilight, the stickler for the rules that she was, insisted on incorporating them into Shining’s character in every game. But still, Shining didn’t understand why he had to play a colt at all.

He continued his complaint: “If we’re playing pretend, why can’t I pretend to be a mare? Or even a stallion?”

Stallion. The word was mostly relegated to history textbooks and speculative fiction. Sure, ponies were generally familiar with what it meant, but nobody used it contemporarily. It was an outdated term from a more primitive time. 

Stallion, a colt that is grown. It flew in the face of the modern understanding that there were no grown stallions, only big colts. And Shining wasn’t even a big colt yet, although his mom had been dropping hints that he might be soon.

Twilight folded up the privacy screen and lowered it. The magical spell that was "narrative immersion" was firmly broken now. No more Crystal Valley, at least for the moment. “Why do you have to be like that?” she asked him disappointedly. “I just want to play a game with my little brother.”

Little brother… Shining was older than her.

As she lowered the screen, Shining could now see her entire upper body, bare breasts and all. Twilight's breasts had recently started developing, though she still had a long way to go before she resembled their mother, or the other full grown mares in their lives. She was completely naked; mares usually were unless it was a special occasion.

A year ago it wouldn't have been a sight worth noting. He saw her naked all the time, just like he saw every mare naked all the time. But recently he'd been paying more attention to her, his eyes lingering longer than he knew was appropriate. But he didn't understand why he felt that way.

It wasn’t the only change that Shining had been going through recently. He may have been in diapers all his life, but only recently had he started to become self-conscious about it. And that self-consciousness was about to get worse, as he felt a growing pressure in his tummy that was making him fidget and squirm. He’d been paying more attention to these belly feelings recently, and he understood what they meant: he had to poop.

He remembered a time when he was smaller and it would just [i]happen[/i], all on its own, and then his mom or Cadance would lay him down and change him. But that was long ago. Now his poops were bigger and he’d feel them in his bottom, growing larger and stronger until they finally started pushing from inside, wanting to come out. He’d usually let them out without thinking much about it… but at least he could tell when it wanted to happen. Cadance told him that was one of the signs of being a Big Colt.

Sometimes it took effort to make the poops come out. He usually ended up attracting an audience when that happened: Cadance, his mom, and Twilight all liked to gather round and comment about how cute he looked. It was embarrassing enough that he’d started debating sneaking off to do his business.

But this poop wasn’t like that. This one felt easy, like he could push it out without even stopping their game. And sure, messing his diaper in the middle of the game was a little embarrassing, but if he was subtle about it he could probably do it without drawing any attention. And that would be much less embarrassing than sneaking off and getting caught, or loading his pants for an attentive audience.

“I’m sorry, Twily. Let’s keep playing.” He did his best to suppress any obvious signs of his body functions. He crossed his legs and sat still, ignoring the bubbling in his belly while he waited for them both to get lost in the game again.

The game continued, but Shining found it hard to focus with the constant churning in his bowels. It didn’t help that Twilight kept steering the game in the direction of his [i]character’s[/i] rear end. Every time the wizard checked the paladin’s diaper, it reminded Shining about his own needs and the pressure trapped in his own body demanding to be vented.

After enough time had passed, Shining decided to go for it. In the middle of Twilight describing the latest trap-filled, monster-infested dungeon room, Shining lifted his butt off the chair just enough that the hard wood was no longer blocking his backside. Puffing out his cheeks, Shining grunted as he felt his body go on autopilot.

Across the room, their babysitter Cadance put down her magazine. “Shining? Are you making stinkies? Does that mean you’re done playing?” She’d been completely quiet up until now, and Shining had honestly forgotten that she was there. Even so, he was amazed how quickly she’d jumped on him. He hadn’t even done anything yet! It was like she had a sixth sense for when boys were doing their business.

Shining stared at her in confusion, but the stare she returned was serious. She wasn’t messing around.

“What do my stinkies have to do with the game?” He asked her. He didn’t mean to echo her foalish language, but he did so on instinct. When it was all he heard from mares, it took conscious effort to not repeat it.

Cadance sighed. “If you make stinkies, you’ll have to stop playing so that you can get changed. Remember what I said? When the poop drops..”

“...The fun stops.” Shining finished the sentence. It was something that Cadance had been saying a lot to him lately, usually in the same sentence as becoming a big colt. Big colts didn’t play games while they were smelly; they had to wait to get changed first. And sometimes they’d be waiting a while. Cadance was very strict about not letting Shining do fun things while his diaper was soiled, even if he wouldn’t be getting a change for a while.

“It’s okay, Cadance, I remember. My poop can wait its turn.” [i]Even if it doesn’t want to[/i], he added in his head.

“Good boy,” Cadance said. “Keep that up, and you’re well on your way to be a big colt~”

Shining beamed at the praise. There was something about being called a big colt that made him kick his legs back and forth and bounce up and down on his seat. Or maybe that was the poop still inside him, activated by his previous pushing and now agitated at having been denied its release. There was still a part of him that wanted to just relax and let go… but he knew if he did [i]that[/i] in his diaper they’d have to stop playing, so he wasn’t about to do that just yet.

But that was okay. He was training to be a big colt, and that meant he could wait.

And so he waited. He did his best to tighten his gut against any more pressure from within, and he focused on playing the game. The wizard and the paladin explored the tower, pushing back the undead menace that had infested it, just as Shining pushed back against the foulness that was brewing in his belly. Shining wasn’t used to holding it in before, and it felt weird, like he was at war with a small part of himself. He knew what his body wanted, but that didn’t mean he had to obey.

Twilight was not oblivious to his distraction. “Are you alright, Shiny?” she asked him after he took longer than normal to decide on a turn. “If you don’t want to play with me, you can just say so.”

“I [i]do[/i] want to!” Shining insisted. “I just… I just…” He glanced over at Cadance, who gave him a subtle, knowing gaze. She knew exactly why he was struggling, and he wanted to make her proud with how he handled it. He really liked his babysitter, and the possibility of disappointing her was unthinkable. He just had to square his resolve and [i]prove[/i] he deserved to be a big colt.

But Twilight could tell that he wasn’t one hundred percent invested, and she was starting to lose the magic. She began picking up the game.

Cadance, her evening’s entertainment finished, got up to make dinner. Shining watched her bare behind disappear around the corner, admiring the curves of her body.

With Cadance out of the room and the game paused anyway, Shining decided that there was no reason to put up with the pushy feeling in his bottom any longer. While Twilight put away the game, he scooted forwards in his seat, lifted his padded rump off the seat, spread his knees, and puffed out his cheeks as he bore down. He felt the mass in his bottom shift; it had only grown heavier in the past hour. Making it move felt like lifting a weight.

It took longer than he had anticipated, because Twilight finished putting the game on the shelf and noticed his behavior. “Shining?” she asked. “Are you trying to make your stinkies?”

“N-No,” Shining grunted between breaths. He didn’t like lying to his sister, but he knew that if he admitted what he was doing Twilight would get Cadance, and Cadance would give him some lecture about being a big colt. The only problem was, why hadn’t his poop come out yet? He was pushing, but now it seemed to want to stay where it was. He could feel some movement though, and his efforts were rewarded with a loud fart that tapered out towards the end, and Shining felt a solid presence begin to poke out of him.

Twilight grabbed his hand and pulled him up off his seat, pulling his attention from his Herculean task. “W-Whuh??” He mumbled. “What are you doing?”

“Come on, mister.” Twilight said. “You just made stinkies so that means you need a change.”

“Wait, h-hang on-!” Shining stumbled after his sister, struggling to keep up and not trip over with the turtlehead poking out between his cheeks. He wanted nothing more than to get into a squat and finish pushing, but found it impossible with Twilight pulling him.

“Uhh, Twi? Shouldn’t Cadance be doing this?” Twilight was clearly gunning to change him, but she’d never done that before, merely watched their mom and Cadance do it.

“Cadance isn’t here right now,” Twilight replied, pushing him onto the changing table that was already set up in the corner of the room. “Besides, if I’m going to be a big mare one day, I’m gonna need to know how to change my colt.”

[i]My colt[/i]. Was Twilight talking about some hypothetical future colt, or was she suggesting that Shining was hers? It wasn't unthinkable. Every colt had a mare who cared for them. Right now that mare was his mommy, and if he ever got married that mare would be his wife. But it wasn't out of the question that he might pass into Twilight's care. He wouldn't be opposed to that either: he loved his sister with all his heart, and she was smart. Even though she was younger than him, she would be a full grown mare one day soon, and would make a great caretaker.

Twilight may have seen him make stinkies in his diaper before, but she hadn’t seen him make stinkies on a diaper before, and now he was racing to make sure she still wouldn’t: as she wrestled with his tapes, he wiggled on the mat and tried to clench the poop in his bottom back inside. He could feel it poking out, sensed it wanting to emerge further, but he fought it. If he could push it, he could pull it, right? 

Straining and grunting, Shining Armor just managed to pull the weight back inside of him before Twilight got the diaper open. The soaked padding flopped onto the changing mat with a wet thud. He could still feel the mess sitting there, just inside. It still wanted to come out, but because he hadn’t done it fast enough, it was stuck inside again. “Stupid poopies,” he mumbled just under his breath. “Why won’t you just do what I want?”

He craned his neck between his legs, trying to figure out what Twilight was doing now. She wasn’t touching him, just looking. Laying like this with his twitching anus exposed to her was something brand new, and if she watched his poop come out, he didn't know if he could live that down. He’d have to hold it in a little bit longer. 

In this pose, Twilight also had an unobstructed view of his penis. She’d seen it before, lots of times. In the bath, or while he was getting changed by Cadance. But she’d never been quite this close to it before. Still she ignored it, her focus mostly taken by studying the wrinkled starfish on her brother’s bottom, and the [i]lack[/i] of butt fudge in his diaper. Shining Armor had baked a brown loaf, she was sure of it. She had been watching her brother all afternoon, and knew her brother’s warning signs and tics. So where was it?

Twilight reached forward with a curious hand. Shining watched her finger disappear from view, blocked by the bulk of his body, and he tensed up. He felt her rest her index finger on his anus, which flexed beneath her touch. His penis twitched too, growing under his sister’s unrelenting gaze.

“Twi, what are you doing?” Shining asked, squirming on the table.

“Checking you, duh” Twilight replied. 

“What’s there to check? I didn’t go!” Oh how he wanted to though. The weight in his tummy from earlier had made its way down to his bottom, and was concentrating in the area around his exit. The only thing that was keeping them inside at this point was the fact that Twilight was staring right at his exposed bottom.

“But you have to go, don’t you?”

Shining didn’t answer.

“Come on, Shiny, just go so that I can put you in a new nappy. Then I can tell Cadance that I’m a big mare for changing my little colt!”

Was that what this was about? Was Twilight trying to prove that she could change his diaper just like mom or Cadance could? And did she really see him as hers, or did she want to prove she could change [i]any[/i] colt and was settling for the closest available? Shining tended to bristle at the thought of “belonging” to any mare that wasn’t his mommy, but if it was Twilight, it wouldn’t be that bad. Twilight may have been annoying and pushy, but he loved her all the same.

But none of that changed the fact that he didn’t want to relieve himself onto an open diaper, and he didn’t feel like he should have to. “Come on, Twily. I’m already wet. Just put me in a dry one.”

“Yeah, but…” Twilight looked askance and lowered her voice. “I kind of want to watch you use it too.” She pouted. “And I know you have to go anyway.”

“What? No!” Shining knew he could get in trouble for saying no to her, but she couldn’t be serious right now!

“Come on, please?” Twilight was giving him the puppy-dog eyes now. Shining hated how he could never resist the puppy-dog eyes. But he had to! This was his butt they were talking about!

Shining felt a sudden pressure on his rear. At first, he thought he was pooping, but that wasn't quite right. The feeling was more alien, more invasive. This wasn't his body trying to push something out. This was something else trying to push its way in.

He felt his anus stretch around the invading force: Twilight's finger. His breathing froze: no one had ever stuck a finger in him before, and it felt weird.

"Ack! Twily! What are you doing [i]now?[/i]"

“Almost…” she muttered to herself.

He knew that look: Twilight was in the zone and there was no point in trying to stop her. He forced himself to take a deep breath and tried to relax. But it was hard; the feeling of her finger probing inside him was weird, and as his entire insides shifted to accommodate the intrusion, he could feel something within him stirring, winding up like a fishing rod reeling in its catch.

Before his eyes, another rod was definitely getting pulled taut. Shining's cock leapt, then slapped against his belly. There was something pooling at the tip, a thin clear fluid.

Twilight watched it happen with a raised eyebrow and pursed lips. "You're not going to squirt, are you?" she asked. She'd seen him squirt during a change before, but it usually didn't happen without his willy being touched.

Shining shook his head. He knew what squirting felt like. "It feels different," he explained. He couldn't describe it. Like something deep inside him was sending tingles up his cock, trying to push something out of it.

“Good. I don't want that thing exploding. It's gross."

Her finger was up his butt, but it was his willy that was gross? Shining felt like Twilight's priorities were off.

Twilight continued to explore his insides with her finger, and Shining did his best to be a good colt and submit. But the wellspring of tension welling up deep in his core made it hard. And he was starting to feel even stranger than before. Twilight pressed up against an unusually sensitive spot inside him, and his cock violently twitched.

Twilight leaned back to dodge the newly animated penis. “Ew, don’t wave that thing in my face! I’m not going to milk it for you!”

“I don’t want you to either! It did that on its own!” Shining’s loss of control over his body was humiliating. Then Twilight twisted her finger inside him and a pained moan burst from Shining’s lips. “Ah! Twilight! If you do that…” But he didn’t know what. His pelvis was uncomfortably tight. He was beginning to suspect that he [i]was[/i] going to squirt, but it was unlike any squirt he’d ever experienced before.

But if his allusions to some unknown shore were meant to discourage Twilight, it had the opposite effect. Her curiosity piqued, she [i]needed[/i] to know what would happen if they kept going. She sped up her motions, digging deeper.

“Twily…” Shining’s voice was needy. “Are you almost done?”

“Just… a little more… aha! Found it!”

Shining felt a sudden force against his deepest reaches. Twilight was pressing on something, driving it deeper into him. “Found what?” he dared to ask.

Twilight was grinning. “Your poop.”

This felt unnatural. How could she possibly be feeling it if he hadn't made it yet? Shining realized that he had never really given much thought to what the poop was like when it was still inside his body. But Twilight was always the more curious of the pair. She'd probably been wondering about doing this for a while.

Why was this making his penis so pokey? He knew what made him pokey: looking at cute mares and having his willy touched. This was neither; it was something entirely new. His cock bounced, the tension in him trying hard to spill out. He shut his eyes and tensed his muscles, trying to ignore the funny feeling that was only growing. .

"Twily, stop! It's too much. I'm gonna squirt!"

That finally snapped Twilight out of it. "You said you wouldn't!"

"You know I can't control it!" Shining couldn't think straight. He knew if he opened his eyes and could see what was happening, he would explode for sure.

Twilight quickly withdrew her hand. Shining trembled, teetering on the precipice. His cock continued to buckle wildly. [i]Please don't squirt,[/i] he begged his willy. He'd be mortified if he squirted in front of her.

The door slid open.

"Twilight! What are you doing?"

Twilight scurried away from her brother, busted. Cadance strode through the door in time to see Shining, on his butt on the changing table, diaper undone, and his hips bucking of their own accord as he battled an impending orgasm. Fortunately, the sudden distraction was enough to pull Shining back from the edge, and slowly the intensity of his hip thrusts subsided.

This was a lot for Cadance to take in at once. “Twilight… can you give us some space?
 She asked. “I want to talk to your brother alone.”

“Oh…” Twilight wasn’t the best at navigating social situations, but even she understood the subtext: her being here was making things harder for them. It wasn’t the first time she’d been asked to give everyone else space.

Shining understood the position it was putting her in too, and he felt responsible. Why did he have to snap at her? A good colt would have just let her do what she wanted. A good colt holds it all in, even his feelings… He laid there on the changing table, disassociating, wondering how the night had gone so wrong.

Cadance gave Twilight her Smarty Pants doll so she’d have something to play with and nudged her toward the door. “Just for a bit, then we can all play together, okay?” Cadance promised.

Twilight nodded and shuffled away.

Now it was just them, a boy and his babysitter. Cadance was technically the same age as Shining, but being a mare meant she was a lot further ahead developmentally.

Cadance started by trying to break the ice. "Is it true you nearly came just from your little sister fingering your ass?"

A sound like choking on water sprang from Shining's lips, and he covered his face with his hands. “Please don’t get mad at her,” Shining said weakly. “She didn’t do anything wrong.”

“I’m not mad at her,” Cadance promised. “And I’m not mad at you either.” Shining was still on the changing table, but he’d pulled back his legs. She put a hand on his knee. “I can tell something’s bothering you,” she told him.

Shining pouted and said nothing. He was already feeling pretty vulnerable laying down naked on the changing table, and if he said anything, she’d just find a way to twist it against him.

Cadance could tell she wasn’t making progress, so she changed topics. She gently lifted Shining’s erect cock in the palm of her hand. “You’ve got a nice big willy,” she told him. “You’re going to make a lot of mares really happy.”

“Mom says the same thing.”

“Your mom’s smart. And she raised a good colt.”

“I wish I wasn't born a colt,” said Shining, crossing his arms and sniffling. He hadn’t meant to be so upfront with it, but when he opened his mouth… it just spilled out.

Oh, thought Cadance. So it’s this conversation. The conversation that every colt eventually has. “Aw, you don’t mean that. What’s so bad about being a colt? You live a pretty cushy life, mister.” She slid her hand under his wet diaper and pressed it into his bottom right as she said the word “cushy,” and Shining flinched as her hand invaded his space. “You don’t have to worry about having a job, or even using the potty! You get to just have fun all day and make us girls change your stinky boom-booms.”

“But what if I want those things?” Shining countered. “I don’t want to rely on mares all my life to feed me, even to wipe my bottom. It’s embarrassing! You force us to do this and then you expect gratitude for it? It’s not fair. I want to have a job like you.”

Cadance refused to dignify Shining’s behavior by taking the argument seriously. “Okay, someone’s being a mister cranky-pants. Colts can have jobs. Your [i]dad[/i] has a job.” Shining’s father worked as an administrative assistant for his mom’s publishing company. “It might not be glamorous, but it’s a big job, especially for a colt!”

Shining was nonplussed. “I mean an important job. One where I don’t have a mare looking over my shoulder all the time and changing my nappies.”

That would truly be something, thought Cadance. She giggled, which was the wrong reaction, because Shining scowled.

“I’m gonna have a really important job one day; just you wait,” he insisted. “Everyone’s going to respect me.”

“I believe you,” said Cadance. “I look forward to it.” The conversation was giving her an idea on how to cheer Shining up. “You know… I can think of something that only colts get to do. Something that’s really important.”

“Oh yeah? What’s that?” Cadance didn’t immediately respond, merely curling her lip into a smile. “Come on, tell me!” Shining knew that he was being wrapped around her finger by this, but he didn’t care. If there was something that made it worth being a colt all his life, he needed to know about it.

“Oh, I won’t just tell you; I’ll show you,” Cadance promised. “But first, you have to do something for me. Something to prove that you’re ready.” She had him hooked, now time to real him in. Her hand which was resting on his knee slid down his body until it pressed against the base of his shaft, still full of life. “I’m going to clean your willy, and you need to hold in your stickies.”

Stickies. Semen. Cum. The inevitable result of getting his diaper changed by a pretty mare. More often than not getting cleaned between the legs would give the growing boy a boner. And wiping that boner down always made him shoot off. Always.

“But I always make stickies when I get changed,” said Shining, suddenly feeling uncertain.

“But you can’t this time, okay? You have to hold back.” Cadance was no stranger to growing boys who had no sexual stamina, but she also knew it was a matter of willpower, and Shining was one of the most stubbornly willed colts she knew. He just needed some courage and some discipline. “Here, I’ll make it easier for you,” she offered. “If you start to feel tingly, like you’re gonna spray, tell me and I’ll stop until the feeling goes away. This is a test to see if you can stay in control. And if you pass… I’ll teach you something brand new.” She took a wet wipe and prepared to clean Shining's groin, but then she added, "Twilight? I know you're listening. You can come back in now."

Twilight poked her head from just beyond the doorway. "I wasn't listening," she insisted. "Um, I mean…" She hawwed, trying to think of a lie.

"Twilight. It's okay. We don't mind that you were spying, do we Shiny? It's only natural to be curious."

Shining [i]did[/i] mind, but he knew better than to correct Cadance when she was speaking for him. "I guess it's okay," he said.

"You want to help me change your brother? It's an important lesson for becoming a big mare."

Most fillies would have been put off by the prospect of an "important lesson." Twilight was not most fillies. She cantered up next to Cadance and stood on her tiptoes, looking over the edge of the changing table at Shining.

"Watch closely, Twilight. It's important to clean up all the pee so he doesn't get a rash. Don't be afraid to touch him wherever he needs to be clean."

Cadance took a wet wipe and gently pressed it against Shining's tight sack. She felt his lower regions tense, his balls pull back close to his body. Shining exhaled sharply as he felt the familiar pleasure.

She ran the wipe up along the underside of his shaft all the way to his tip, and she felt his hips buck and heard him hiss. 

"I'm gonna squirt," he warned her.

Already? How cute. If this were a normal change for a little colt, Cadance knew what she would do. She'd cover the tip of his cock with the wipe and let nature take its course until the wipe was full of sticky seed. But they were trying something new today, so instead she pulled her hand away and watched his cock twitch in the cold air. "No you aren't," she told him. "Deep breaths, okay? You can do it."

"...okay." Shining knew he was being tested. He focused on his breathing and felt the urge recede again. It helped that he wasn’t as close as the first time.

Soon Shining had calmed down, and Cadance offered a wipe to Twilight. "You want to try?"

Twilight looked between her encouraging caretaker and her blushing brother. “Okay,” she said. She took the wipe and positioned herself over Shining’s lower body. “But he better not squirt on me.” She still thought that was gross.

“He won’t, will he?” Cadance promised, prompting Shining with a nod.

“Yeah, I won’t make stickies,” Shining promised. He didn’t know if this was true or not, but he wanted it to be. He didn’t want to deal with disappointing [i]both[/i] of them.

Twilight was mesmerized by Shining’s shaft and the way it moved. “It’s like a snake,” she muttered. She especially liked the thin bit of liquid beading at the snake’s “mouth”. She pressed the wipe against the tip to wipe away his pre-cum, then grunted in discontent as he just made more of it. She tried to wipe it up again, then gasped as Shining's willy bounced against her hand. She knew it twitched during changes, but there was a huge difference between watching it happen and feeling it react to her touch.

“You doing good?” Cadance teased.

Shining wouldn’t give in that easily. “I’m okay,” he promised. Really, he felt like he was riding the edge constantly right now, but he couldn’t just tell them that!

Twilight took her time cleaning him. On one hand, her pauses gave him time to cool back down. But he hated how stretched out this was. He always squirted during changes, and he always would, so why were they dragging out his torment? Just go faster, he silently pleaded, and either he succeeds or he fails. Either way, it would be over.

“All done!” Twilight announced, feeling rather proud of herself.

Wait, really? She’d finished? He’d made it! He’d just been cleaned with a stiffy without blowing his load!

“Well would you look at that,” mused Cadance. “Guess you really are shaping up to be a big colt after all.”

Shining beamed with pride. Making them happy made [i]him[/i] happy.

Cadance continued: “Alright mister. A promise is a promise. You ready to learn a brand new thing that only big colts do?” She reached out a hand and pulled him upright.

Shining looked down nervously at the changing table and his naked body. “Um, aren’t you going to put a new nappy on me?” It was risky letting a colt run around without a diaper. He’d been stuck in a situation like that on occasion, when the family ran out of diapers and his mom had to run out to get more. Usually it turned out fine, but sometimes… he shivered as he recalled his punishment.

“Nope! We don’t need nappies for what we’re going to do.” Cadance crossed her arms and frowned. “Why, do you feel like you need one? Are you planning on making poopies?”

“No! Of course not!” Shining quickly stammered out. “I don’t have to go. Well, I mean, I do…” Both girls already knew that. “...But it’s all going to stay inside me, I promise!”

Cadance helped him off the changing table. “You know, that’s a very big-colt thing you just said,” she told him.

He tingled from the praise. ‘It is?”

“It is. Every colt makes poop, but only little colts need to let it out, you know? Big colts know how to hold it.”

Huh. Shining had never thought about it like that. “Hang on, does that mean that I don’t need to wear nappies anymore?” He knew that girls stopped wearing diapers after a certain age, but every colt he knew was still always padded. But if he could hold it, were they really necessary?

Cadance laughed like he’d just told a joke. “You need to wear protection when you’re out in public; that’s just common sense. But tell you what, if you’re a good boy for the rest of this, I’ll let you go without nappies at home. But if I see any poopy on the floor, I’ll tan your hide.”

Shining’s heart skipped a beat. “Okay,” he said, his voice shaking. He could feel the weight in his bowels. It wasn’t moving, just waiting. He could keep it there… right?

“I mean it. Being allowed to go without a nappy is a [i]big[/i] responsibility. If you don’t think you can handle it, tell me now.”

“I can handle it!” Shining promised. If he could do that, that would change his life!

“Good.” Cadance put one hand on each sibling’s shoulder. “Now, who’s ready for their first grown-up lesson?”

The atmosphere in the room was full of excitement as both filly and colt cheered. Shining’s earlier anxiety was all but forgotten now.

“Should I be taking notes?” asked Twilight.

“Nah. There’s no way you’re going to forget this,” promised Cadance.

“Um, Cadance? What exactly are you going to teach us?” Shining couldn’t help but sense that they were about to cross a threshold.

“Isn’t it obvious?” Cadance was pumped. “You’re going to fuck your sister.”

[i]TO BE CONTINUED[/i]