Stage 1) Sam turns the wrong corner, and the werewolf gets the jump on him.
Stage 2) Sam very literally stumbles back into the motel room fifteen minutes later, breathing heavy, bruised, bloody, eyes blown wide and trembling a little because he knows, he knows what this means, and the only thing he can get out after Dean rushes to his side, equally scared, and Sam recoils away from the touch, is “I got bit”.
Stage 3) Dean, of course, is adamant that they’re going to find a way out of this, because they always do, it’s what they goddamn do.
Stage 4) Except what do you know, Sam does turn.
It wouldn’t be immediate. There’d be a good portion of time there before he really turns, where he’s starting to feel weird in a whole lot of ways but still has control. Still has say over his mind. One of the first things to show up is a heightened sense of smell. He’s getting these urges, too, these urges that he’d never admit out loud, that he’d hardly even let himself think in the light of day and yet here they are, pushing themselves into his conscious and he can barely even stop them. Bad urges. Really fucking carnal urges. Dirty urges, wrong urges, all involving his brother.
And they just get stronger by the minute. And pretty soon Sam’s freezing, looking sick, looking horrified, realizing, holy shit, he just might actually follow through on these urges if Dean doesn’t tie him down right fucking now.
So he tells Dean as much, whilst omitting the most vital and incriminating details.
“You better tie me up tight,” and, “I’m serious Dean, tie me up good.”
And there’s this weird fear in Sam’s eyes that Dean doesn’t understand, because yeah, fear over killing innocents is one thing, but there’s this edge to Sam’s voice he hasn’t heard before, and something about it makes Dean’s spine crawl.
So he does. He ties Sam up good.
And Sam, of course, continues to change. He’s still in control, but Sam can feel that control slipping. He starts sweating. He starts breathing harder. He tugs at the restraints. There are a few moments, too, where something slips through, something foreign and unnerving to Dean, where Sam just looks at him, and it’s the way Sam looks at him that makes the hair on his neck stand on end. He can’t tell what emotion Sam’s feeling, exactly, but a little later on Dean does recognize part of the expression, and when he does, it’s fucking terrifying seeing it there: the look is predatory.
And then, Sam does something really goddamn manipulative, and Dean falls for it completely. Sam feigns pain. He sucks in a breath, shudders, curls in on himself, lets out a noise like a wounded animal that’s just distinctly Sam enough to really freak Dean out, and Dean should have realized something was wrong, should have realized that’s not part of the turning process, but he doesn’t, because Sam’s in pain. He’s over in an instant, getting way too close, getting right up in there in Sam’s space, foregoing safety completely because something’s wrong.
He honestly doesn’t register the next few seconds, except for rope snapping and something huge and heavy slamming into him and the world tilting sideways.
“You smell delicious,” is what he hears next, right up next to his ear, right up near his neck, too close, way too fucking close, and he can’t move, because Sam’s pinned his goddamn hands down.
And so of course, Dean being Dean, he copes the only way he knows how.
“Gross, Sammy, c'mon. Friends don’t eat friends.” It comes out confident, languid, teasing in a brotherly way, except there’s a thin vein of fear in his voice he can’t shove down and honestly? He’s scared shitless. And he’s pretty sure Sa– whatever Sam is now knows it too.
Except then Sam. Sam.
He makes this weird, freaky purring noise, and Dean’s brain temporarily shorts, because wait, aren’t werewolves a dog thing? Why is he fucking purring?
“Wasn’t what I was planning on.”
And that? That honestly takes Dean a few seconds to get.
Dean goes stone still, then, his breath frozen in his chest, the words echoing in his head, bouncing around, like something’s snapped, like there’s a short or something, and they just won't compute because-- no, no fucking way.
"Sam?" His lungs feel like lead. It comes out uncertain, small, horrified and doubtful, and then Sam's-- Sam’s-- he’s licking, right underneath the shell of his ear and Dean sucks in a breath, sharp, ice cold, jerks ineffectually underneath his brother, but he can't move, he can’t-- "Sam."
There’s real fear in his voice.
But Sam just hums, languid and content and pleased in some sick, dark, fucked up way and then he nuzzles lower, grip vicelike, breath hot on Dean’s neck, and Dean's heart feels like it might just burst out of his chest as Sam leans forward, pressing his lips--
"S-Sam, jesus, stop!"
Sam wasn't listening.
Dean turned his head to the side, not to goddamn accommodate but to look away, to grasp desperately at the inch or two of space available to him, to breathe, sharp and shallow, as his gut clenched with nausea, because this-- this wasn’t Sam. This wasn’t Sam.
A low growl seduces him back to the present.
"Why don't you make me." And then Sam bites. Not enough to break the skin, almost enough to break the skin, enough to make Dean shout, and Dean chokes down another noise, writhes--
And Dean, he tries. He really does.
He kicks out, twists, throws all his weight into it, and for a half a second he thinks he might have accomplished something, that maybe, maybe, if he bends just right and hits not-Sam just there-- but then he’s hitting the floor hard, painfully, getting the wind knocked out of him worse this time, and it takes him half a second for it to consciously dawn on him why.
He’s on his stomach. Sam flipped him onto his stomach. Sam was behind him, on top of him, and Dean was on his stomach.
“That’s better.” Sam says, smug and feral and satiated. And Dean? Dean might actually throw up.
"S-Sam. Sam, man, come on, I know you're in there some--where!" His belt snapping breaks off his sentence. And then Sam yanks his hips up, and Dean scrabbles at the ground, because no, no--
He chokes down a cry-bordering-on-sob as his pants are all but ripped off. And then Sam’s back at his ear, too close, breath hot, everything hot, and Dean can’t even flinch away.
"Come on, it's not the first time you've been in a position like this," he all but fucking croons. Dean nearly chokes.
"Not as subtle as you think you are," he grunts. And-- and you know, if Dean wasn’t already fucked up over everything else happening right now, wouldn’t that just be the icing on the cake. Because fuck. Fuck.
Then Sam’s moving again, grabbing Dean’s wrists, wrenching them behind his back, and of course-- of fucking course he struggles, he tries to fight, he bucks, but now his muscles are screaming at him, they hurt, and there’s a thick, jagged lump in his throat that’s hard to breathe around and he can feel a fucking breeze on his thighs, and so if Dean doesn’t wrench himself around as violently this time fucking sue him.
Or at least, that’s his stance until two seconds later.
Because two seconds later, Sam’s fingers-- they’re behind him, low, really low, tracing up over his boxers with a sickening sensuality, touching the one scant-ass piece of clothing he has left, the one barrier keeping his ass from the world, from Sam, and dipping underneath them, yanking them down--
But it’s too late.
Sam growls again, sounding hungry this time, and Dean flushes hard, goes painfully red, can’t breathe, his breath coming fast and dizzy and making him lightheaded so fast he almost doesn’t notice the next thing Sam does. Almost doesn’t. Because who the hell wouldn’t notice slow, hot breath against the cheeks of their ass.
“Sam,” he starts, voice barely above a whisper, paralyzed, breathless, because this-- intimacy-- sex-- that was one thing, but this-- “Sam, you’re not gonna--”
Apparently, he was gonna.
Sam gets his face in there -- Sam gets his face up in Dean’s ass -- and licks, a long, broad, hot, wet stroke, and Dean jerks underneath him, violently, shuddering and shouting out like he’s been whipped, because oh, fuck, oh god--
“Sam--!” Sam drags his tongue across Dean again, moans carnally, and tongues him harder, verging on-- christ, verging on tonguefucking him, verging on actually sinking inside, and Dean shouting turns into a strangled, breathless cry, his chest pistoling up and down as he thrashes so hard he feels sweat beading. Because fuck. “S-Sam, fuckingnnngg--!”
And then Sam does push inside in one too-warm, spit-slick glide, and Dean twitches, chokes, his mouth falls open but he loses all verbal function, because Sam, because his baby brother, because Sam’s tongue is in his ass and it feels like he’s been gutted and there’s some stomach-churning, horrible heat stirring to life inside him too, one that he can hardly acknowledge, one that’s familiar and he knows that sends cold dread pooling in his gut, in his veins, everywhere, because no, no. Not now, not with Sam. Not like this.
By the time Sam pulls back, satiated with his work, lips red, his brother trembling and tense with exhaustion and adrenaline, Dean’s loose and pliant and wet and hard and more sick and ashamed of himself than he’d ever been in his entire fucked up life. Because this wasn’t hot. This was sick. This was wrong, it was horrible, it was a goddamn nightmare and the only saving grace was that when Sam woke up tomorrow he wouldn’t remember a single freaking moment of it.
He hears a zipper being undone, denim being pushed down, and he knows, he knows this is going to hurt like a bitch, hurt worse than a bitch because spit isn’t lube, but what can he do? What the fuck can he do?
A noise catches in his throat when he actually feels a hot, slick something press and slide against the entrance of his ass, and he squeezes his eyes shut against the wetness in them. His hands are numb.
“Not like this, Sam. Please.” It’s a whispered plea.
Sam nudges his hips forward. Dean sucks in a shuddery, shaky breath as he feels pressure, and then more pressure, and then feels himself opening slowly around-- around Sam’s--
“Sammy.” Begging, now. “Not like this.”
Sam fucks half his cock into Dean in one sharp, careless, fluid motion, and now Dean feels the pain. It’s a miracle the noise he makes doesn’t draw any neighbors.
It hurts. It hurts. Not-- not like a hunt gone wrong, not even like his first time, which is fucking bizarre because his little brother is a lot bigger than his first fuck, but it hurts and now, now he feels gutted, now he feels fucked open and raw, now he feels-- feels--
What was-- how the fuck was he so wet? Sam’s pulling out, rocking himself in, pushing further, fucking him deeper, and all Dean can think about over the sick, sharp, nauseous bloom that’s settled low in his chest is why doesn’t it hurt more? He knows bullshit hentai tropes. He knows how real sex works. And then something dawns on him. He can’t exactly turn to face Sam, but he can tilt his head, and he does, and his voice is raw but he gets the question out.
“Are you-- did you--?” Did he just come? Because it was the only thing he could think of that might make things… smoother, even if it made no sense ‘cause Sam hadn’t even paused, but not-Sam only snarls and leans forward and presses him harder against the floor by the neck in response -- his shirt slides up, exposing his midriff, and the new angle makes his own flushed cock bump against his stomach with each thrust, and fuck -- and yeah, okay, he definitely hadn't come, then. He was definitely still going.
Dean grunts against the dirty motel floor as Sam pistons inside him, rocking him, thrusting him forward, each fever-hot glide stretching him further and stirring up newer, biting pain, until finally, finally, Sam gives one last, final surge (Dean gasps roughly, worn to the bone), and he’s in, he’s pressed up inside him to the hilt, Dean’s full, way too fucking full, and Sam’s balls slap against his ass like some particularly filthy note of punctuation at the end of a fucked up sentence. Dean shudders. Sam purrs.
And then -- then. Dean thinks maybe he’s imagining things. Thinks maybe he’s hallucinating. Thinks, at first, maybe he’s finally fucking cracked, because his brother’s a werewolf, his brother’s fucking him, his brother’s balls deep inside him, but no, no, Sam’s--
Dean jerks underneath Sam, panic rising, because what-- what the fuck--
Sam’s getting bigger.
“S-Sam, you’re--” Sam shoves himself one last, impossible inch deeper. Dean can’t breathe. “Sam!”
There’s pressure, and then more pressure, and then more pressure, and Dean thinks he deserves props for not losing his fucking mind, because what the actual FUCKING fuck-- he can’t-- Sam’s-- oh god, Sam’s--
Sam’s coming. Sam’s coming a lot. It’s pouring into him, Dean can feel it gushing, filling him, slick and warm and wet, and where his cock had been brushing his prostate before, now it was pressing, hard, harder, relentlessly, and Dean, he can’t-- he can’t--
"Ah-- god, fuck, stop, stop--"
He comes, hard.
He’s a trembling, shaky, unresisting mess by the time it’s over. ‘Cause it hadn’t been over after Sam came. It hadn’t been over after Dean had been wrung dry and come the first, second, or even third time. It’d been over after what felt like ages, after he’d been pumped full of so much come he swore he could feel the weight of it in his belly, after Sam-- after Sam actually could pull out, because for a while there he was just too freaking big. His knees felt skinned. His entire body radiated a bone-deep ache. When Sam finally pulls out in one long, wet slick of movement and releases his hands, Dean doesn’t move, just lets them drop to his sides and then stays there, face pressed against the floor, breathing, eyes almost shut but not quite, letting the quiet wash over him. Because what was the point. It was already done. And besides, he wasn’t entirely convinced he could move. Not yet.
He’d have to move before morning. Before Sam changed back. But he could do that. He’d have to do that.
Walking might be a different matter, but he’d think of something. He’d have to think of something.