Sam wakes up, bleary-eyed and irritable because he had nightmares last night that he can't quite remember but which still remain, lying beneath the edges of his sub-conscious with impressions of sharp teeth and flames. He looks over at Dean, a reflexive reaction that's part reassurance that the most important person in his life is safe and part reassurance that his big brother is there to keep him safe from the nightmares, real or imagined. Because Dean always has, ever since a serious six year old would tuck a chubby two year old into bed at night with the solemn promise to kill any monster that dared to crawl out of the closet, he'd 'use a knife, see, here it is right here, Sammy.'
Settling a little at the sight of the unmoving lump of blankets that says his brother is right where he's supposed to be, Sam sits up, rubs the sleep out of his eyes and stumbles out of bed and into the tiny motel bathroom where he lets the steaming heat of the tiny shower unwind his knotted muscles. He uses every last bit of hot water because he needs it today and, also, because, well, Dean was kind of a dick yesterday—more so than usual anyway—and, hey, payback's a bitch.
Feeling refreshed and maybe even human he exits the steamy bathroom and then stumbles back with a yelp, clutching instinctively at the small white towel covering not very much actually, as he stares at the girl, the outrageously pretty (and pretty much naked) girl sitting in Dean's bed. Sam is enough of a guy that his eyes wander south and he notices she's got perfect breasts, B cup looks like. They're perky and her skin is amazing; smooth, silky and tanned and his eyes take it all in before gentlemanly instincts kick in and he whips his gaze back up to fasten firmly on her face, not that looking at her face is a hardship 'cause wow, seriously gorgeous. The girl yawns and stretches her arms up in such a way as to show off the said breasts (that he's really, really not noticing) in a very impressive way.
Sam looks frantically away from the naked girl and scans the small room for Dean—how the hell did his bro sneak a girl in here last night without waking him, anyway—but doesn't see his soon to be ass-kicked brother anywhere in the room. So Sam looks back at the naked girl, focusing desperately on her eyes—EYES Sam, focus the fuck on her eyes—and watches the girl frown, blinking long-lashes framing sleepy green eyes. A feathery cap of honey brown hair frames a model gorgeous face with slashing cheekbones and pouting lips and…oh fuck, Sam feels his eyes widen as a horrible feeling starts in the pit of his stomach even before the girl gives him a casual 'what the fuck?' look of inquiry and opens her mouth to inquire in perfect Dean speak 'Dude, what the fuck are you looking at?'
At that point Sam can only point wordlessly at his brother (sister?) while still instinctively clutching at his towel even though he's been naked in front of Dean plenty of times throughout the years—hell, Dean likes to remind Sam he used to change Sam's diapers when he wants to be especially annoying—but Dean had never been a girl before. Dean frowns again, then follows the direction of Sam's finger which is pointing directly at—"What the FUCK!" Dean jumps straight up out of the bed and in the back of his mind Sam is deeply relieved that Dean's at least wearing the boxers he went to bed in last night although they sure as hell fit differently this morning than they did last night.
"What the FUCK!" Dean repeats again, a little hysterically, and really Sam can't blame him because he's feeling a little hysterical himself although a part of him that, yes, okay he will admit it, is a petty bastard, just takes note of his brother (sister!) clutching his/her? arms in front of—oh the hell with it, her then—breasts in a classic modest maiden pose because, man, when this is all over, he is sooo going to have something to hold over Dean that is way worse than having had your diapers changed.
When Dean shouts "What the FUCK?!" a third time in an increasingly high register, Sam decides to helpfully point out "you're a girl, dude."
This response is, of course, not received well at all and Dean's shouted semi-hysterical response is along the lines of "I can fucking see that, you fucking moron!" and "I am going to find the fucking creature that did this to me and I am going to fucking bitch slap that mother fucker into the deepest, darkest fucking hell there is!"
Yup, any doubts Sam may have had that this is a prank are laid to rest because that…that was definitely Dean.
"Why aren't you a girl?" Dean yells at him accusingly, reaching down to pull the sheet up in a jerky, graceless motion, clutching it around her like a cloak.
Sam shrugs and doesn't even bother hiding the smirk because, okay yes, this is serious, but dude really…this is also funny as hell.
"Wipe that smirk off your face asshole or you'll be smirking without the teeth I'm gonna knock out of your friggin' head," Dean hisses and Sam stops smiling because Dean may be serious. Although…
"Would the breasts throw your center of gravity off in a fight?" Sam asks, genuinely curious, and then feels his eyes widen involuntarily at the sulfurous round of cursing that erupts, creative and long and very, very vicious.
Eventually Dean stops swearing long enough to pull a t-shirt shirt on for which Sam is profoundly grateful because, being fascinated by your brother's breasts is just wrong, wrong, wrong on so very many levels. Dean sits at the tiny table in the corner of their motel room and settles down to brooding in dark silence, no longer swearing continuously, instead just muttering an expletive every minute or so like she's managing to stomp down the self-knowledge of her new girldom for just that long before it resurfaces and she has to curse her fate anew.
"Okay, what could have done this?" Sam asks practically because although there is the element of amusement, in the end this just one more freaky thing the Winchesters need to deal with, like psychic visions or vampires.
"How the hell do I know?" Dean mutters resentfully, still not quite over the freaking out part although he's starting to deal, Sam can see it in Dean's eyes. Which, geez, Dean had had absurdly long-lashes as a guy but as a girl they're ridiculous, like some exaggerated painting of femininity and yeah, that thought, he's keeping to himself because center of gravity off or no, Dean would kill him dead.
"Well…we didn't fight anything last night and we were tracking a ghost of a killer dentist. Hard to imagine him turning you into a girl for kicks."
"Then what was it?" Dean asks, using surly to cover up the desperation starting to glimmer around the edges because God fucking dammit he does not want to be a girl. He feels off in his own skin because it's not his skin. He's got these breasts bouncing around in front of him and he loves breasts, he always has, the soft giving feel of them, the sounds he can wring out of women when he's paying devoted attention to them with his calloused fingers and his clever tongue but not when they're attached to him. He feels weak and there's a hot gush of panic that just keeps flooding his stomach because he feels…violated. He's not him anymore. Someone or something did this to him and he is going to kill whoever…whatever did it with a smile on his face and a vicious song in his heart.
Sam must finally be registering just how freaked out Dean really is because he looks at Dean, serious suddenly, losing the amusement that he'd barely bothered to hide and that had made Dean consider hitting his baby brother very, very hard. But now Sam's mouth has taken on a grim line and he's sincere—no one does sincere like Sammy—as he says "don't worry bro. We're going to figure this out." And some of the panic fades a little because they will figure this out. It's what they do. And Sam and Dean together, they don't fail.