Based off a prompt received in a comment on AO3:

Could I possibly request a slim castiel x fat! Almost immobile Dean? One where he's panting alot trying to get around, maybe to show Castiel that he's still able to move like he used to but Castiel is super skeptical but can't really refute Dean's claims as technically he is still able to waddle around

The first time it came up (where Dean could hear it, at least), it didn't register. Honestly, he didn't even realize that Castiel was talking about him.

He and Sam talked about so much stuff when they were together, most of it nerdy, and they got even nerdier when Sam, off consulting on a hunt or doing research, called from the road. Castiel and Sam were a lot of things, not least among them the two absolute most important people in Dean's life, but they were also both geeks of the absolute highest degree. Could've put Steven Urkel to shame. As a result, he tended to tune them out when they really got going, for everybody's best interest.

That time was no exception. Dean was pretty deep into killing waves of zombies, video games being one of several things he'd discovered an intense and abiding love for in retirement, leaning over without taking his eyes off the screen to sip from the straw of the extra-large milkshake that Castiel had placed next to his easy chair. Castiel's voice was a distant, comforting hum from the kitchen, like rain on the window or Sam's breathing back when they'd used to share motel rooms. Dean barely heard him.

"Well, I don't know. He definitely can't see his feet anymore, I can tell you that for sure."

Dean didn't make the connection the second time, either.

"I would put it at…I don't know. Ten thousand calories a day, perhaps? I could judge more accurately, if you would like me to - oh. Oh, yes, I understand, I suppose that would be 'weird.'"

Or the third.

"I've thought about it myself. Simply what it would look like if he tried to, say, climb a fence now…yes, you're right, it probably would break the fence."

In fact, Dean didn't realize - and everything else didn't click in his brain - until he heard one undeniable detail that pegged it all to him.

This time, he was watching TV. Beer at hand, party-size bag of Chili Limón Lays at the other, Dean had settled in to watch the Jayhawks. First game of the season. Castiel was set to join him, but then Sam had called, and Castiel didn't like or understand baseball well enough for Dean to pause it, so he'd gone ahead and started without him. Over the crack of the bat and the smooth rhythm of the announcer's narration, Dean could hear him in the other room.

"From how difficult it is just to walk, not to mention how much he's eating, I would imagine it will be any day now," Castiel said casually. "Certainly before you get home." A pause. "Yes, of course I've planned for it. I've had plenty of time, he hasn't been able to fit in the Impala for months."

Dean choked on a swallow of beer, and stabbed for the remote. His fingertip, greasy, slid off the button the first couple times, but he managed to pause it eventually. Planting his hands, he huffed in a breath and, with effort so intense he literally felt sweat popping out in round little beads on his forehead, he heaved himself up out of his easy chair. Well, not so much a chair as a repurposed loveseat, but Dean was pretty sure the thing had been closer to chair-size no matter what the label said. What with the way it pinched his hips and all.

Breathing hard, he slowly made his way to the open-plan entryway to the kitchen, walk a rolling waddle. He planted a hand on the wall for balance, panting, and demanded of Castiel, "Excuse me?"

Castiel, compact and unshaven in the sweaters and jeans he'd started favoring since retirement, paused, turning blue eyes on him. A second passed, filled with the ragged huffs of Dean's breathing. Then he said, "I'll call you back," into the phone, hung up, and set it aside.

"You…are excused," he told Dean slowly. Dean rolled his eyes. Castiel still had some trouble catching the exact drift of English turns of phrase, but there were also times when he was just intentionally obtuse. As Sam would say.

"Cut the crap, Cas, I heard what you were saying to Sam," he said. "You were talking about me, weren't you? What've you planned for?"

Castiel squirmed. Of course now he was tactful, for the first time in his life. Dean, still wheezing every other word, gestured impatiently for him to get on with it. The pizzas he'd had for lunch were sitting a little heavy in his stomach, and he'd really like to get his ass back in his chair.

"When you're unable to move," he said. "On your own, or otherwise."

Dean stared, then snorted, shaking his head and looking away.

"This is all Sam, ain't it?" When Castiel didn't respond, he repeated the demand. "Ain't it? Fucking health nut, I know I've put on a few since we settled down and all, but I'm not that fat."

He waited for Castiel to agree. Because Dean knew that he was a certified fatass these days, fried foods gathering in an impressive beer gut (which was the only reason he couldn't fit in the Impala, all his gain was centered in his middle and they didn't make 'em for big boys back in '67), but it was just comfortable middle-aged spread. Nothing to worry about. Definitely nothing that would pin him in place, like those people on TLC, stuck in beds and wheelchairs, undergoing surgery just for a shot at a normal life…

Dean was fat. But not that fat. Not immobility-fat. Not medically fat, as he thought of it. And Castiel was about to tell him that.

But he didn't. Instead, the silence just kept stretching on, and on, and on, only Dean's breathing and the occasional belch punctuating it. He couldn't help getting annoyed. His feet were absolutely killing him.

"Am I?" he demanded.

"There's nothing wrong with it," Castiel hurried to add. "Between Sam and I, we can keep you healthier than you ever were when you…weighed less, and it isn't as if you're unhappy, and…" The expression on Castiel's face suggested that, if he were human, he would have been blushing. "I like it."

Cue another roll of Dean's eyes. "Yeah, I'd figured that one out, Cas." What with all the thigh-fucking and belly-squeezing and tit-sucking in bed. "And I'm sure glad you do, but - son of a bitch. You guys have been talking about me for ages, haven't you? How fat I'm getting? What, Sam tell you to put me in a scooter?"

Castiel hemmed and hawed. Dean had never actually heard anybody do that, but it was all the answer he needed. He huffed, shaking his head and wiping at his brow. Sweat flung away.

"Unbelievable."

"Dean, how much do you think you weigh?" Castiel asked him, a little uncertainly. Dean shrugged, and felt himself jiggle.

"Jesus, Cas, I don't know. You bought that stupid tiny scale, remember? Can't see the damn thing."

"Ah." Castiel cleared his throat. "Well, last we weighed you, you were nearing six hundred and fifty pounds."

Dean looked down at himself. Because there was no way it could possibly be that much, Castiel was pulling his leg. He calculated, taking stock: big, plush moobs snuggled in a faded, stretched Zep tee, dotted with pizza sauce and chip flavoring and other, older stains. Thick, soft arms with creases at wrist and elbow rather than the bony swell of joints. An ass that, when he touched it, he could feel straining against the seams of the 4XL pajama pants he was wearing. And a big, soft, doughy overhang of belly, swelling out far past his chest, past his feet, dusted with freckles, pale and creamy, so large he couldn't see his belly button, so large he wouldn't have known where it ended if it weren't for the near-liquid sway of the weight when he walked.

Yeah, okay. Maybe he was pushing 650.

But he was not immobile.

"Fine," Dean said, and smoothed a chubby hand over the velvety expanse of his upper belly. He didn't miss the way Castiel's eyes followed it. "But there's pure muscle under all this." He flexed one arm, and swallowed the wheeze that lifting all those rolls forced out of him, blood thundering under his jaw. "You're not sticking me in a hospital bed with an oxygen tank anytime soon."

Castiel folded his arms over his chest, and said nothing.

"What, so I can't - run a five-minute mile anymore, or kick a door in," Dean said defensively. "Doesn't mean I'm too fat to walk."

"Dean," Castiel said, with the infinite patient of the immortal, "I don't think that you can even make it to the front door anymore."

"Oh, fuck off!" Dean exclaimed. "We literally just went out for breakfast this morning, dude. What, your vessel's brain on the fritz or something."

"I flew you to the van."

Dean stared, then said, "The bar last night."

"We flew."

"The buffet last week."

"Flew."

"Okay, Sam's anniversary party."

"Every time you have left the house within the last six months," Castiel stated, "it has been under the power of my wings."

Dean paused. He drummed plump fingers against the wall, thinking. Then he jabbed one at Castiel and said, "Bet you one of your - no, three of your PB&J cheesecakes that I can make it to the front door."

Castiel's chin lifted at the mention of his rarely-constructed but oft-craved signature dish, and Dean knew that they had a deal even before he said, "I accept the terms."

Dean grinned, feeling his cheeks squish and his chins wobble, and began to slowly turn. Castiel's next words gave him pause, though.

"But, Dean? No breaks."

He blinked, swallowed, then recalled the grin. "Well. Duh."

Dean turned himself, slowly. Swaying from side to side, hip bumping plushly into the wall over and over again as he did so. It was hard, doing this without being able to see his feet; tough to maintain his balance, especially because he'd had fucked-up knees to begin with, and all Castiel and Sam's angel-witch shit hadn't done a whole lot to help with the natural consequences of that. He didn't want to roll an ankle.

It was slow going. But finally, he was turned fully around, and there was the front door. White-painted wood. Cute little curly-cue suburbia glass insets on the top and sides. Straight shot between him and it.

Dean's toes curled against the floor. There was already a spot of sweat on his T-shirt, right where his tits met each other. His breath heaved in and out of him.

But he was Dean goddamn Winchester. He'd survived Hell. He could sure as shit make it to his own front door.

One foot in front of the other. Slow swing to the side, belly wobbling, thighs rolling off each other, and then the other came heavily down. Yeah, this wasn't so bad. Two more steps, and Dean could literally feel Castiel's gaze burning a hole in his back; he looked over his shoulder, dragging his chins across his chest, and yep, there he was, still standing there. Staring at him.

With what looked like a pretty impressive tent in those jeans. Ooh, they were so going to talk about that later.

It didn't start getting really hard until about the halfway point, when Dean passed his loveseat. That was the point when he realized that the first half had been easy, which seemed really, super unfair to him, because come on, he was so soaked in sweat by now that his ass crack squeaked when he took a step.

His breath coming in and out of him sounded like somebody trying to start up a particularly surly chainsaw. He wavered, staring down at the loveseat. At its oh-so-inviting cushion, with the personalized ass groove and everything. It would be so easy to just throw himself back down, watch the game, drink beer, let it go…

He glanced over his shoulder again. To Castiel. Who had taken out his phone and was literally, actually filming.

A white-hot spike of spite, of the kind that you could only feel for people you well and truly loved, punched up through Dean's sizeable stomach. He flipped off the camera, turned around, and kept going, blowing and sweating.

Fuck Sam. Fuck Castiel. They could kiss his wide ass, both of them. And never mind the fact Castiel would probably enjoy that.

There was one shaky second, where Dean overcorrected a little, the pendulum of his great, soft belly swinging a little too far and leaving him in the adrenaline burst of wobbling on one foot, the other in the air, toes grasping like he could grab the carpet with them, arms pinwheeling. Insomuch as they could, with how exhausted and sweaty he was. Castiel was instantly there, reaching out to steady him, but Dean pulled himself out of it and irritatedly waved him off with one meaty arm. Knowing Castiel, he'd count helping him out like that as a forfeit.

"Back off, Florence Nightingale," he stated. "I'm fine."

And he was. Panting, wheezing, wobbling, rivulets of sweat running down him to collect in already-soaked clothing and drip into the floor, Dean reached the door. He even did Castiel one better: he grabbed the handle with one very wet, thick-fingered hand, squeezed it open, grabbed either side of the doorway, and then shoved himself (the front part, at least, which ought to count for all of him if you were rounding up) out into the bright, clear Kansas air with a whoop of triumph.

Beaming, he twisted his head on his neck to look at Castiel, who was right there.

"Yeah," he said. "Woo! I win! I fucking won, in your face, I made it, I can too get to the front door, what do you fucking say to that, birdbrain?"

It didn't quite go like that. More like Woo - huff - I - wheeze - win - groan - and so on, but Dean felt the spirit made it through.

"Well, you did it," Castiel said, after a short pause. "You're not immobile."

"You're goddamn right." Dean smirked. "Now get me my goddamn cheesecakes."

Castiel hesitated, then headed for the kitchen. Dean watched him go, twisting his head far enough it hurt his neck, dizzy and breathless with relief and also the intense exertion of walking roughly a dozen feet.

In another minute or two, Castiel would realize that he was well and truly stuck in the stupid doorway. Hopefully sooner. With the way it was squeezing his belly, Dean was starting to kind of worry about restricting the blood supply.

But right now, all that mattered was the sweet, sweet taste of victory.

Which didn't even taste half as sweet as those cheesecakes were going to.