Author's Note: So this just kind of happened. I guess there's hints of Destiel, but it's just adorable fluff… literally. Enjoy!

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"Oh man, I HATE that guy!" Dean fumed as they departed from the empty warehouse.
"Gabriel is irritating, I agree." Cas replied seriously from the back seat of the Impala.
Sam snorted. "That's an understatement."
The rest of the car ride went by quietly, and soon they pulled up in front of the motel. The three of them got out of the car and made their way to the room, where they settled down for the night. Dean flopped onto his bed gratefully, while Sam took up residence at the small table, clicking away on his laptop. Cas (as usual) stood stock-still and vacant at the end of the unoccupied bed, staring at the far wall. Dean rolled over so he was facing the angel.
"Somethin' wrong, Cas?"
The man in the trench coat turned his startlingly blue eyes on the hunter. "I'm not-" suddenly he doubled over, his hands flying up to clutch his head. An unnatural noise burst forth from Cas's tightly clenched teeth. "AHHHG!"
Dean leapt off the bed and raced over, along with Sam, who had accidentally tipped over his chair in surprise. Together they guided their friend onto the mattress while he writhed in pain. The brothers could only watch in horror, not knowing what was going on with the angel.
Then, without any warning, Cas disappeared in a puff of white smoke, leaving a puddle of trench coat and suit behind on the bed.
"Cas?" Sam asked worriedly, looking up.
Dean grabbed his brother's sleeve, directing his attention back to the bed.

The pile of clothes was moving.

Immediately, the two of them drew their guns and aimed at the writhing lump. Something small was struggling out of the sleeve.

Something small and fluffy.

The brown tabby kitten tumbled ungracefully out of the sleeve, trailing Cas's navy blue tie around its tiny neck.
"Is that..." Dean stared at the kitten. "Is that Cas?"
The tiny creature looked up at him, apparently recognizing the name. His eyes were still the same shade of bright blue.
Sam crouched down beside the bed, face to face with the cat. "I think so."
"Holy crap."
"Mew."

Sam, being the research expert, got to work immediately. After about two minutes, he realized that the kitten wasn't likely to stop pouncing on his fingers until they stopped moving across the keyboard, so Dean was charged with keeping Cas entertained. The elder Winchester scooped the kitten off of the table and carried him over to the bed. There he sat, staring up at Dean and flicking his small tail back and forth across the stained bedspread.
"What?" asked the hunter, put off by the staring.
"Mew." Cas answered, clearly unimpressed.
Dean, unsure of what he should do, picked up the discarded tie and tentatively dangled it in front of the kitten's face. His whiskers twitched once, and then the furry little thing launched himself at the piece of fabric. Dean kept it just out of reach of his tiny paws, and the unfortunate kitten tumbled right off of the bed, landing in a heap beside the man.
"Heh. Sorry, KittyCas." he said, and planted himself on the mattress. Cas jumped up beside him and began to wash his paw, pointedly ignoring Dean.
Not really knowing what else to do, he reached down and gently scratched behind one of the kitten's ears, and marveled at how soft his fur was. Cas stilled his licking and cast an eye towards Dean, but made no move to pull away from the touch. On the contrary, he seemed to lean into it, which the hunter found encouraging. After a few minutes, the kitten was on his back, paws in the air and purring like a tank. Dean was grinning like an idiot.
"Sammy!" he whispered urgently, not wanting to alarm Cas. "Sammy, look!"
The younger Winchester swiveled around in his chair and smiled. "Aw, he likes you. Hmm. I wonder if Cas is still in there, or he's all cat?"
Dean shrugged, massaging the happy kitten's soft belly. "Dunno. Why d'you ask?"
"Because you're basically rubbing him down."
The elder brother turned to scowl at the younger, and did so until he turned back to the computer. Then Dean lay back on the bed and picked up the kitten, placing the small furry animal on top of his stomach. Cas immediately snuggled down into his sweater, and before long his eyes drifted shut. Dean then realized how busy the day had been, how tired he was, how warm Cas's furry little body was and how much he needed a nap. He promptly fell asleep with the cat curled up on top of him.

Sam snapped a picture with his cellphone.
...

The moon was up when Dean opened his eyes again. There was a piece of paper taped to his forehead that read "Went for dinner, be back later -Sam", and light weight on his chest that went with the feeling of fur under his chin. A smile found its way to his lips when he glanced down at the still-sleeping Cas. He really was very cute as a cat. Dean brought his hand up and gently ran his fingers along the kitten's spine, chuckling when he cracked open an eyelid and began to purr. Soon, the fluffy kitten was stretched out on top of the hunter, purring so loudly that Dean could feel it in his chest.
"You're very friendly as a cat. Why can't you be like this all the time, Cas?"
This earned him an offended meow, and a furry tail in his face.
"Aw, come on, I didn't mean it."
Dean smiled again as the kitten rounded on him, and marched purposefully up to the hunter's chin. Cas stared into his eyes for a moment before raising his right front paw and very pointedly batting Dean on the nose.
"H-hey!" He laughed. "What was that for?"
The cat looked at him as if to say "like you don't know". Dean tried to look apologetic, but Cas wasn't buying it. Finally, he gave up and lifted the kitten off of his chest and onto the mattress, fully prepared for the silent kitty treatment. After stretching, the hunter got up off the bed in search of a drink of water. Apparently Cas wasn't happy about being ignored, because suddenly there was the familiar sound of feathers beating the air, and something landed on Dean's shoulder. Cas meowed in his ear.
"Alright, KittyCas. I apologize, okay?"
The kitten meowed again, then nuzzled the spot just below Dean's right ear. However much of the angel was in the cat, it must have been slowly losing out to the feline side, because human Cas would never be caught showing affection. As they wandered in the kitchen together, Dean hummed "Eye of the Tiger" softly. Cas seemed to appreciate the humor, because he purred happily into the hunter's ear. He leapt onto the counter after Dean placed a bowl of water there for him. But unsuspecting of the slick surface, and unused to his clumsy kitten limbs, Cas slid right over the other side. Dean dove around the counter; arms stretched out to catch the poor guy, and somehow in the process knocked the bowl of water off and sent it flying. Both cat and man were showered with water, but Cas remained safe clutched in Dean's arms.
They looked at each other for a moment, stunned. Then Dean burst into laughter at the kitten's damp and bushy fur. He quickly stifled his giggles at the un-amused look on Cas's face, and then gently placed the kitten on the counter.
"Wait here for a minute; I'll go get a towel to dry you off."
"Mew." He sat down obediently before beginning to lick his paw.
Dean returned shortly holding a plain white towel from the bathroom. He refilled the water bowl, and then set to work drying off the kitten. He wrapped Cas in the towel, and began to vigorously rub the fabric against the cat, which elicited a long string of purring from the bundle. About two minutes later, the towel was removed, and there standing in its wake was the puffiest little furball Dean had ever seen. Not to mention the cutest.
"You should see yourself right now, KittyCas." He said with a grin. "I'm going to put on some dry clothes. Can you entertain yourself for a few minutes?"
As an answer, the kitten began to make work of lapping up the water in the bowl. Dean made his way over to his duffel bag and fished out a pair of sweatpants and a dry shirt. After changing into those, he pulled on his warmest sweater and a pair of socks, feeling decidedly chilly. He then returned to the kitchen, bringing a dry towel with him to mop up the rest of the water. This time when Cas poofed onto his shoulder, he only smiled and continued to wipe up the spill. Shortly after that, Sam entered the room, carrying a brown paper bag that smelled delicious.
"Is that-?"
"Bacon cheeseburger," Sam answered, anticipating the question. "And a can of tuna for your shoulder-cat, if he wants it."
The man and cat wandered over to the table where Sam was seated. Cas teleported to the tabletop, wary of jumping, while Dean settled into the other chair. He de-lidded the can of tuna for the kitten, and then set to work on his own meal.
"So," he said after a mouthful of cheeseburger. "Any luck with the lore?"
Sam shook his head. "Nope. Sorry Cas."
The kitten lifted his head from the can long enough to look delighted at the discovery of tuna, which caused the brothers to chuckle. Clearly the fact that he was a cat didn't seem to bother Cas that much.
When the food was gone, and the small mess cleaned up, Sam and Dean decided that there wasn't much they could do about the situation, at least not for the night, anyway. They agreed that in the morning they would call Bobby for help, and for now the three of them would get some rest.
Sam drifted off quickly, as usual, but Dean had trouble finding sleep, probably due to the nap he had taken earlier. Cas hopped up onto the bed, wobbling around as the mattress gave way under his legs. He let out a soft meow, which Dean interpreted as asking for permission. Silently, the man reached out and pulled the kitten to his chest, rubbing his soft ears gently.
He cared for this little creature very much, and the angel stuck inside him even more so.

Long after the elder Winchester fell asleep, he murmured words that only the kitten was awake to hear.
"My... My KittyCas."

The next morning, Sam was the first to awaken. He got up, showered, dressed and made coffee. Dean still slept, blissfully unaware, with a kitten curled protectively in his arms.
Sam snapped another picture, which would later end up as the wallpaper on Dean's cellphone.
Hours later, the three of them were on the road to Bobby's house. They had recently swapped seats, and now Sam was driving while Dean sat in the passenger seat with Cas curled up in his lap. No one bothered pointing this out because it would just cause trouble. They had called Bobby earlier in the day, telling him about the problem. A few choice words had promptly been hurled at them via speakerphone. After he simmered down, Bobby promised to get to work on the lore, and told them to drive to his house anyway, because they couldn't exactly keep a kitten on the road with them. Then, a few hours later they had gotten a call from the man, saying that he had managed to rustle up a potential spell.
Now they were pulling into the familiar gate. They exited the car, with Cas perched on Dean's shoulder-one of the kitten's favorite spots, it seemed. Bobby snorted at the sight of the fluffy angel-kitten, and then led them into the study, where a large leather-bound book sat open on the desk. After an intense match of Rock-Paper-Scissors in which Dean employed his winning anti-rock theory, Sam was put to the task of performing the spell.
Five minutes and a puff of white smoke later, Sam was a moose.
Cas meowed in either annoyance or amusement, while Dean facepalmed and Bobby muttered "idjit".
The moose looked balefully at his brother, who noticed the small envelope tucked into Sam's left antler. He walked over and plucked it out, stepping back quickly when Sam's huge nose approached his face. Dean opened the letter and read it silently, growing more furious by the word. He could practically hear the smarmy voice.
"Don't mess with the bull, or you get the horns. Or in this case... The antlers. Cool your jets, Dean-o, the spell will wear off soon. Just having a little fun at our brothers' expenses. Hugs and kisses,
-Gabriel"
"That little BASTARD!" Dean thundered.
Bobby slipped the note out of his hands and read it as well. "Figures," he grumbled, eyeing Sam warily. "It's exactly the son of a bitch's style."
Dean sighed and plopped down onto the couch, jostling Cas from his shoulder onto the cushion. "Sorry KittyCas," he said immediately, scooping the indignant kitten back up into his arms. "So now what?" he asked, directing the question at Bobby, who had also dropped into a chair.

"We wait it out. There's not much else we can do."
Sam the moose, apparently having registered the whole exchange, huffed noisily and then lay down in the middle of the floor, soon drifting off into a giant-moose slumber. Bobby threw a large plaid blanket over him, and then bid Dean and Cas goodnight. The only human Winchester settled into the couch, laying on his back and listening to the footsteps retreating up the stairs. He placed Cas on the back of the sofa, draped a blanket over himself, and then replaced the kitten on top of his chest. He sandwiched the cat under another blanket, because Bobby's house got cold at night. Soon Cas began to purr, and Dean watched his beautiful blue eyes blink shut. The kitten's head dipped down, his chin resting on Dean's chest.

In the early morning, Dean woke up squished. He couldn't move, and when he cracked an eye open, he saw a head of dark hair just under his nose. Cas was back to human form, luckily still sandwiched between two blankets, because he was probably naked. It didn't really bother Dean that much, and he stayed there contentedly, with the angel's face pressed into his chest. A while later, he pried his arms free to relieve some of the heat, but the movement woke up Cas. The man raised his sleepy face, and their eyes met.
"You're back," Dean said quietly.
"Yes." The angel answered. "Dean, I... Would you..?" He asked a silent question, unsure of what to say.
Dean circled his arms around Cas and started to run his fingers through the angel's soft, sleep-mussed hair. "Go back to sleep, KittyCas."
And he did.

Sam was a moose for two more days. Bobby crashed into a wall when the younger Winchester changed back.

….

And Cas never told anyone... But he was himself the whole time.

…...