"Why don't we watch some TV to pass the time?"
"I guess..." December unenthusiastically shuffled over to the spot on the couch his sister was pointing to and sat down with a crinkle, holding his stomach the entire time.
"That laxative is going to take a while to work, but when it does, I want you to just push and let it all out, no questions asked." October pointed to the absorbent padding her little brother was now wearing. "That's what the diaper is for."
"Okay, big shis," the shiny Kirlia said with his usual braces-induced lisp.
The shiny Gardevoir turned the TV on, tuning it to the channel that ran all of those educational little kid shows her brother enjoyed but was a little too old for. She then kissed him on top of his head and left the room, calling behind her, "Let me know when you're done, okay?"
"Okay..." December sighed. "Thish ish what I get for holding it for two weeksh," he muttered to himself as he rubbed his bloated abdomen.
The young Kirlia frowned. It felt so weird to be wearing what was pretty much a full outfit, minus any kind of proper bottom. He still had the purple bows in his hair, and he was still wearing his purple t-shirt with the big lilac heart in the center. He was still rocking the knee-high purple socks with the silver snowflake pattern, not to mention the silver heart, star, and snowflake charm bracelet he usually wore on his right arm, as well as the rainbow of assorted silly bands he wore on his left.  Heck, he was even wearing his white light-up tennis shoes with the purple laces. Conspicuously absent, though, was his usual pair of purple panties, let alone any skirt or shorts. December blushed as he looked down at the fluffy, purple disposable diaper with white trim that was the only thing that covered his privates. Oh well, at least the white snowflake pattern ot it was cute.
Honestly, he would have been fine with just sitting on the toilet and doing his business there, or even going on a pad bottomless, but October insisted that a load as big as the one he was holding onto would clog the plumbing something fierce. And while going bottomless on a mat would give him plenty of room to push everything out, the cleanup would be way too messy. This really only left the "wearing a diaper in the living room" option that he currently found himself taking. He shrugged. At least he got to watch TV this way.
- - - -
After getting through an episode of "Clifford the Big Red Arcanine" and half an episode of "Beartic in the Big Blue House", December's bowels didn't feel any closer to moving, but his bladder was about ready to burst.
"October!" the preteen Pokemon called out, squeezing his legs together as he fidgeted.
"What is it, Li'l Sis?" the Gardevoir replied from the other room, invoking her usual teasing nickname for him. "Are you finished already?"
"No! I haven't even gone yet!" He kicked his legs back and forth as he squirmed, setting off the pink and purple lights in his shoes as they hit the front of the couch. "But I gotta go pee real bad!" he whined.
"Um... you do realize you're wearing a diaper, right?"
"Oh!" The Kirlia's eyebrows raised in surpise. "I can pee in thish?"
"Oh come on," his sister replied, "I wasn't gonna have you put on a diaper and crap in it, and expect you to not pee as well."
"Language," December chided. He looked down. "I dunno, I guessh it jusht feelsh kinda weird to go pee in thish thing on purposhe..."
"Look, don't get up, okay? Just go where you're sitting. That diaper will hold it, trust me."
"If you shay sho," the Kirlia replied. He uncrossed his legs, sat back a bit, and relaxed his aching bladder.
"Ohh," he moaned in relief as a warm stream immediately started pouring out of him and into his thirsty diaper. He looked down and smiled as he peed out the several cups of apple juice he had had at breakfast. Maybe it was the sheer joy of relief, or maybe it was the novelty of peeing while sitting on the couch and watching TV, but whatever the reason, December couldn't help but grin as he let loose, the diaper growing puffier and squishier with each passing second. Just barely over the sound of the TV, he could faintly hear the quiet trickle that accompanied his pee as it rushed into the absorbent padding, eventually causing the part of the garment between his legs to also become damp, puffy, and warm. He giggled as the wet warmth trickled to the bottom of the garment and tickled his privates. 
Eventually the stream slowed to a dribble, then to a drip, and finally to a stop. December sighed, having finally finished. Oddly enough, he actually felt pretty good for a grade-school kid who had just peed his diaper, his continued constipation notwithstanding. His sister was right: the garment had indeed done an excellent job of containing the flood. A good deal of the diaper, mainly the front of it and between his legs, was puffy, darker-colored, and heavy; it had absorbed it all, though, leaving nothing but a warm and pleasant dampness around his privates, and little bit under his butt. What's more, the mild smell of ammonia wasn't even bothering him, much to his surprise. A big smile spread across his face as he continued watching TV in relative relief.
- - - -
It was towards the end of "The Topsy Turvy Show" when the little Kirlia's gut finally decided it was time to empty. Those Inkay brothers had just managed to visit the microbrewery for the very first time when December felt the bloated fullness in his bowels start to move downwards; he gulped in anticipation. Heeding his older sister's words, he didn't hold back at all. He simply shifted position in his warm, wet seat, leaned forward a bit, and pushed, letting nature finally take its course.
For a few seconds nothing seemed to happen, the only sound coming from the end credits playing out on the TV. With a little straining and pushing, the young psychic-type managed to force out a long, low fart, followed by a quiet crackle as he finally succeded in squeezing out a fat, solid turd, a foul odor filling the air as the log squished beneath him into the warm, damp paddding around his butt. His face flushed bright red as he continued straining, and he grunted as he managed to push out another turd, adding a sizeable amount to the mound forming in his diaper.
December stopped for a few seconds to catch his breath, then quickly resumed his pushing. Leaning to the side a bit to make room, he moaned as yet another firm log snaked out under him, bringing the pile in his pants nearly to the size of a squished grapefruit.
He stopped again and panted. He certainly felt better now, but he knew he was nowhere near done; given how long he had been holding it, there was surely more on the way soon.  He sat back up, blushing as the squishy warmth of the load in his diaper pressed up against his butt. The little Pokemon actually thought it felt rather good, like sitting on a warm pile of play dough, only a hundred times stinkier. He giggled at this thought, then started to return his attention to the television, when he was suddenly stopped by a loud gurgling from his intestines.
December's eyes widened as he realized that "soon" meant "now", and he gritted his teeth as a flow of softer poop forcefully squeezed its way out of him even as he sat upright. He leaned forward again, crossing his arms in front of him and squeezing them against his belly. He moaned as the mess crackled out of him faster into an ever-growing bulge in the seat of his diaper.
Suddenly feeling another urgent need, December instinctively shifted to a slightly reclined position , leaning back as another torrent of pee streamed out of him into his already wet diaper. This time,  more of the bottom and back of the diaper was hit by the flood, those areas starting to puff out as they soaked up the new onslaught. All the while he continued dumping his load, the soft mess squeezing between his legs and up against his privates. 
"Uggghh," December groaned as he closed his eyes. Pushing out all of that solid mass was certainly wearing out the young Pokemon, and the smell was just awful, but he had to admit that the rapid relief to his weeks-long ordeal felt good in a way.
Soon the flow died down, and with a final push, it was over at last. December opened his eyes and sat up on his squishy and warm seat. The diaper he was wearing was soaked, and all between his legs and beneath his butt was a thick, squishy load of poop that stunk to high heaven, but the little psychic Pokemon had never felt better. A bright smile appeared on his flushed face. "All done, shish!"