Brother Issues

A/N: Part of the Chocolate Box Exchange Round 1 on AO3, written as a treat for Taste_of_Suburbia, combining the pairings and prompts of Sam/Dean mutual pining and Dean/Lucifer with Lucifer caring for Dean because he's his brother's vessel and courting him.

A/N2: Although nothing more intimate than kissing really happens, Lucifer is possessing Sam throughout most of the story, so if dubious consent issues due to identity are a problem, be warned.

Sam hadn't really meant to say yes. He'd just had a spectacularly bad day at the end of a generally crappy stretch of days. It had been his idea to part ways with Dean, but – well, it was done now. After those idiot hunters had come back to the bar and started a fight, after he'd had that dream of Jess that turned into a nightmare of Lucifer? He had needed to do something to get all the ugly thoughts out of his head. Unfortunately, what he'd actually managed was just to get himself stupid drunk. Somewhere along the line, the thought had floated through his head that since he'd pretty much already fucked the whole world over by letting Lucifer out of the cage in the first place, he might as well finish the job, right?

Lindsey had long since scampered off, all thoughts of trying to learn any more about Sam's mysteries gone. Sam had come back after hours and broken into the liquor stash behind the bar, tossing a fistful of bills into the register to make up for the damage. Somewhere between sobriety and drunk enough to pass out, he'd thought it was a good idea to start berating angels in general and Lucifer in particular to the empty air. Apparently, saying yes in the middle of a drunken rant sarcastically was good enough for one of those bastards, because the next thing Sam knows everything is obliterated in a blast of white light.

After that, well, after that, Sam is a passenger in his own skin. Jimmy Novak had described being an angel's vessel as akin to being chained to a comet. Sam got the comparison, but it wasn't really how he would have described it. There was at first an overwhelming sensation of being crushed behind a burning cold presence. Stretches of indeterminate time passed and Sam almost felt he was drowning under that massive, overwhelming being. Then suddenly, he'd be looking out his own eyes again, but he was never in control of what was happening, only able to watch what Lucifer wanted him to see or hear what the angel wanted him able to hear.

The first few times they interacted in any way, Sam was pretty sure Lucifer was taunting him, though the angel didn't actively address Sam. For the first stretch of forever, Sam assumed now Lucifer had what he wanted, he wouldn't be bothering with the mind of his insignificant human vessel anymore. He'd thought his glimpses out of the body's senses were incidental, but he'd been discounting that Lucifer created the demons and there was nothing they loved more than playing with their victims. It isn't until he's looking into the face of someone vaguely familiar with black eyes and feeling Lucifer's anticipation that it all comes together.

"Is that my prom date – Rachel something, I think?" Along with the thought, he feels a sudden spike of rage.

The sense of smugness suddenly coming through loud and clear from Lucifer only exacerbates his anger. "What's wrong, Sam? Didn't you realize just how many watchers Azazel had, making sure you stayed on the right path? Since I don't like them any better than you, why don't we do something about it?"

It's only a few seconds later and he's watching as the angel tears both the vessel and what remains of the girl within apart. Most of Sam is appalled, but there's just enough of an angry little jolt of satisfaction for him to feel guilty about. Doubly so when the smugness from Lucifer only amplifies. It's the first demon from Azazel's army wearing a face from his past they obliterate, but it's nowhere close to the last.

After that, sometimes Sam randomly gets feelings he recognizes off the angel, though often he can sense Lucifer reacting to something but whatever the thoughts and emotions are, they're too immense and alien for Sam to quantify them easily in human terms. Rarely, the angel addresses him directly in their shared mind space or even out loud. As they move through more and more demons, at first Sam curses and rails at the overwhelming presence to stop, but gradually the burning cold of the angel and its indifference to and occasional amusement at his pleas leave him too numb to be bothered. Lucifer's emotions remain strange and inhuman most of the time, and Sam was left vaguely feeling as if he was being poked at like a child prodding a bug with a stick to see what it would do.

When Sam stops reacting to the slaughter of demons wearing old familiar faces, the angel showed him Pestilence, busy at work concocting an old nightmare. Then he called Death from Outside and chained the horseman through the murder of an entire town population of possessed – people and demons alike snuffed like candle flames in the space between eye blinks. He can't even sense any strain from Lucifer, only appeasement and perhaps a tinge of excitement. When Sam refused to rise to the bait and react to any of it doing his best to conceal the horror he felt under the despair that Lucifer was going to end the whole world soon enough anyway, Sam was left in the dark for another of those indeterminate stretches of nothingness. He has no idea how much time has passed, other than it feels like it's been too long already.

The next thing he's allowed to experience is the angel letting him listen in on a phone conversation with an unsuspecting Dean, agreeing to meet up with him and get back together to figure this apocalypse thing out. From what his brother says on the phone, it's clear that the stretch of time that had felt like forever to Sam had been but a short stretch of days in reality. Despite his growing feelings of apathy and despair, Lucifer interacting with Dean was something Sam couldn't stop his reaction to. But it didn't make any more difference whether he screamed angrily or begged desperately, the only reaction he got in return from the angel riding him felt most like a vague and distant condescending amusement.

Lucifer drives out to meet up with Dean in the middle of nowhere. If Sam had any control over his own body, he's sure his heart would be pounding away in fear as Lucifer lets him see Dean leaning casually against the Impala's side as the body they're currently sharing slowly walks over. He doesn't expect Lucifer to reveal himself right away – that would be too easy. Still, he's a little surprised he can't really decipher any particular emotions from the angel as they both listen to Sam's brother given a whole big speech about why they should reunite.

Dean was wrong. Dean is sorry. They are both each other's greatest strength and greatest weakness and they keep each other human. As his own voice makes promises to work with Dean, Sam can't decide whether he wants to laugh or cry. Why the hell could Dean not have figured all of this out just a few days earlier when it still might have mattered? And what the hell is Lucifer's game, playing along? Just how much is he going to drag this out to torture Sam? It's not like Sam wants to watch Lucifer kill his brother, but seeing Dean so close to danger and completely unaware makes him ache in fear down to the depths of his soul. Worse, he still can't get any kind of read on what Lucifer is thinking or feeling now.

They head out in the Impala to a hunt Dean apparently had his eye on and Sam is constantly torn between mentally screaming for Dean to buy a clue and hoping he doesn't because then his brother will be dead. He doesn't really believe Dean can save him from this, but somehow, without Dean, he knows that's when it'll really be over. There's a vague sense of annoyance building from Lucifer gradually, and he finally addresses Sam when Dean is off paying for gas.

"Sam, I'm your real family, we've always been destined to be together. I want you to truly understand what you are. Your parents, Dean, they were just a foster family, that's why you always wanted to get away. I'll show you. When you see how fast Dean gets disgusted and gives up on you, we can finally move forward to our great destiny."

Sam doesn't mean to respond, but Lucifer's words bring a slew of memories rushing in. How Dean would rather have died with him when he was infected with Croatoan. How Meg possessed him and tried to get Dean to kill Sam, but even under the weight of a promise to their father, Dean refused. That Dean sold his soul to bring Sam back and Bobby's voice telling him Dean had been willing to let the demon win and the world burn before he'd made that choice because he just didn't care with Sam gone. Hell, right now, here Dean is asking Sam back after the whole disaster with Ruby that let Lucifer free to begin the end of the world. Sam can't help but think Lucifer is really off the mark, because he's not sure there's anything that could actually make Dean leave him for good. The thoughts barely register before he's buried under a blanket of rage and suddenly he's not being allowed to use the body's senses anymore. He's terrified of what the angel might be doing to Dean and if it was possible to scream himself hoarse in his current state, Sam would have passed that point long before he's allowed to see again.

When between one moment and the next, Sam is suddenly aware of the outside world again, he tries to brace himself for whatever might be happening outside his head. He doesn't expect Dean to be dead, because he's sure Lucifer would want him to watch that, but he knows there are plenty of things nasty enough you can inflict on a human that they can still live through.

Lucifer's thought echoes through their shared space to him, chastising Sam's thoughts. "I would never harm my brother's vessel, Sam." He doesn't understand why the strange tinge of disdain flavoring the thought seems to be directed both at both of them, so he dismisses it. He thinks he has a fair grip on Lucifer's emotions some of the time, but his inability to understand the rest of the time leaves him with some doubt about what he does think he's feeling.

Cautiously taking things in, Sam doesn't know what to think. Dean seems fine. Okay, so there's a certain wariness around his eyes directed at Sam that makes him seriously wonder what's been happening in the interim, but that's all. There's nothing about the expression that makes Sam believe he actually suspects Sam isn't the one driving Sam's body.

The more Sam is allowed to see, the more perplexed and worried he gets, because Dean seems committed to trying to reassure "Sam" in terms that are kind of terrifying. They'll be working a case and Dean will come out with something like, "It'll be okay. It's not your fault." Those sentiments get repeated fairly often, and then late one night in the motel room as he's going to sleep, "I'll help make sure you don't hurt anybody else, Sammy."

It can't be about Ruby, he's pretty sure, because Dean is still mad about that. Yeah, he pretends to be over it, but Sam knows his brother and can still see a hint of anger even when he avoids the subject. So that leaves a whole host of uncomfortable questions. God, what has Lucifer been doing in his body?

Things only get progressively more confusing after that. Sam had assumed Lucifer allowed him awareness again because he'd gotten tired of playing with Dean. So he keeps expecting an explosive revelation that never comes. Then he wonders if Lucifer is going to try and groom Dean into saying a yes of his own, somehow, but Michael never enters into their conversations. The angel doesn't even do much subtle hinting about how hopeless their chances of stopping the apocalypse are. Instead, Lucifer insists on showing Sam random bits of his own life, as it carries on and is lived as if Sam himself were still living it, which is confusing and disturbing as hell because it makes no sense.

Lucifer doesn't let him see everything, just random snippets he can't figure out the reasoning behind. He watches himself offer to go get the coffee several mornings. He sees his brother's face light up when Lucifer brings him his favorite kind of pie, and listens to Dean thanking him for remembering (it's not like Sam ever actually forgot, he just "forgot" to mess with Dean). Volunteering to do extra research on hunts by himself without complaint. Washing the car. At first, Sam thinks Lucifer is making some kind of dig about how Sam's a horrible brother. Which would be weird enough, and doesn't fit in at all with what Lucifer said he was doing. A slight hint of exasperation from Lucifer and the sensation is gone again, so Sam just keeps watching, frustrated and confused.

He watches Dean being Dean. Teasing what he thinks is Sam, and pouting when Lucifer responds like Sam would. Jumping straight into the line of fire on hunts when something goes after Sam. Insistently trying to check injuries to Sam's body when Dean himself is bleeding profusely from a cut on his forehead. Half-teasing, half-proud when Sam comes up with the answer to a case (sometimes via actual Sam's thoughts on it, since Lucifer doesn't much care about insignificant creatures like the monsters they fight). Through it all, Sam tries to figure out what Lucifer's game is, shouting imprecations into the big empty space of their shared mind, but nothing more that feels human enough to understand comes back through.

It's not until he has to watch, completely disconnected from the physical sensation, as his own hand runs gently down the side of Dean's face that he understands the angel has seen far deeper into his mind than Sam thought and is definitely taunting him, but not with Dean's death. He's sure now that Lucifer's game is to drive Dean away by exposing how Sam has always felt. How could Sam not be in love with Dean when Dean had been his whole world growing up? When Dean had been the only real solid rock in his life after the world he built for himself at Stanford exploded into flames leaving nothing but ash? It's so long been his deepest, darkest shame that Sam was sure it had been buried deep enough Lucifer wouldn't even see it, because Sam had never been willing to risk that Dean might find out and either treat him with pity or actually finally leave him behind willingly. Lucifer managing to ferret it out isn't his worst nightmare come true, because even his nightmares hadn't been quite that cruel.

When Dean pulls away from the touch, eyes wide and startled, muttering something awkward about hustling and all but fleeing the room, Sam's consciousness curls up into a miserable ball in the corner of his own mind and vows not to watch anything else. It's exactly what he's always feared, and it hurts so deeply he can't even get up the ire to scream at Lucifer about it. He doesn't even try to figure out what the angel might be thinking, he can't be bothered to care.

Sam isn't the one who controls what he sees and doesn't, however. And he's forced to watch, not only as Lucifer makes more and more overtly romantic gestures to Dean, but as Dean, bewilderingly, actually starts to accept them. Lucifer sits too close on the same bed or at a rickety table in one motel and the first few times Dean pulls away nervously to pace, only for Sam to see him the next time staying right where he is, Lucifer making sure Sam can see where their legs are touching though any physical sensations are still denied him. Dean stops shrugging off one of Sam's arms being thrown over his shoulders or around his waist when they're just sitting around or walking somewhere. The day he watches Dean's lips part and eyelids flutter closed as Lucifer leans in to kiss him, it's too much.

He'd been angry before when he was sure Lucifer was trying to drive his brother away, and he's even angrier now but he's angry this stupid angel is kissing Dean with his body. Doing, without compunction or doubt the thing Sam spent most of his life too afraid to do. Not only doing it, but getting a positive response from Dean, who still thinks it's Sam? That day is the hardest Sam fights to try and overthrow his unwanted occupant since that first day after being possessed. It doesn't work. Lucifer was waiting for it, and Sam can feel him laughing at Sam's struggles. Beyond the pure wordless amusement the angel doesn't offer any commentary, though, and Sam lives in dread of what he'll have to watch next.

He's prepared to have his heart completely broken, but weirdly, Lucifer never takes things much further than that. There are a few more kisses, that if not exactly chaste, don't progress even so far as really making out. Lucifer starts pulling back, acting gradually unhappy and distant until finally he starts putting words on Sam's tongue he'd never speak. Words about how he hadn't really wanted this, he'd just wanted Dean to accept him back. That now he remembered why he'd been so eager to go to Stanford, to go to Ruby; Dean could never learn to let go. Dean was suffocating him. Dean had never been good enough to be his equal as a brother, let alone anything more, Dean could never see far enough to be on Sam's side. The problem is, in his own head, Sam not only knows all of that to be the opposite of the truth, he hears every repetition of Dean's name ring with another's underneath. Michael. Run throughout with a whirling mishmash of emotions – anger, taunting, righteousness, even confused affection – those might be the words, it's all too huge and too confused for Sam to really grasp and it doesn't really matter in the face of what the words are doing to his brother.

Dean sits through the accusations stoically, until Lucifer stops talking out of Sam's mouth. There's a long pause. Finally, Sam isn't sure which breaks his heart more, the tears built up in his brothers eyes or the way he just apologizes for the wrongness of his feelings, of his actions, of never being good enough for anyone to want to stay. Dean cannot hold the eyes of Sam's body for any of it, and he finally says that if Sam wants to go, he can go, if he wants to stay Dean will do whatever he needs to do, just give him another chance. He's hidden the wrongness of his feelings for years, he can do that again if Sam will just stay. When his brother is done speaking and has turned away, where there had before been that strange turmoil, now Sam can only find a weird alien feeling he's come to identify as curiosity.

Maybe that's part of it, but it certainly can't hurt that as desperate as he has ever felt before, Sam needs to overpower Lucifer right now, almost as much as his body needs air. What the angel might say next could shatter his brother in a way that nobody could ever put back together again, and Sam won't allow it. He slams every bit of will and affection he has for Dean against the massive cold presence in his head, screaming the words until suddenly, somehow, Lucifer is pushed back and they're spilling out his lips, "No, no, no, Dean!"

It's been months since Sam was able to feel or control his limbs, so his rush towards Dean is more of a comical stagger, but it doesn't matter, because he's only a few steps away from where Dean is sitting on the edge of a ratty motel bed and then he's there, pulling Dean into his arms. His brother stiffens at the touch, but Sam won't let go, rushing to get out the words in a barely decipherable jumble, "I'm sorry, so sorry. I had to - I can't explain – just whatever happens, you have to know I love you, Dean. Same way you love me."

He knows there's no point in trying to warn Dean about Lucifer, and he can already feel the angel pushing hard to get back control. There's not a damn thing Dean can do; they don't even have an angel blade with them, assuming that would even work on the devil, or that Dean would do it to Sam's body. So the only thing Sam can do is make sure Dean knows he's not alone, that if Lucifer is going to kill Dean and destroy the world by Sam's own hand at least his brother will know how he feels.

He's still wrapped around Dean when Lucifer pushes him aside again, and Sam waits, angry and sick, to see what's going to happen now. He hasn't been paying any attention to Lucifer's thoughts or feelings, and it's not until he no longer has the distraction of his own senses that he feels a strange mingling of regret and affection. Affection that weirdly, he recognizes as one of those background feelings he hadn't been able to really decipher, buried and masked for a while now by his own feelings for Dean. It's confusing and though he doesn't actually ask a question of the angel, his bewilderment gets an answer.

"You still really understand very little, don't you? I saw what God had made and I could not understand why he created such petty, flawed beings. And then my own brother tossed me away at our father's words. I still love him, I still don't understand, but I've seen more. You're not as tiny as I thought you were, nor as important."

Sam's confusion only deepens, and before he can try and formulate a response, their mutual attention is drawn back to the outside world, where a teary-eyed Dean has pulled away, his face wet and his brow furrowed in worry, "Sam? Sammy, what's going on?"

"Dean, the eldest." Lucifer puts his hands to either side of Dean's face and Sam is horrifyingly sure Lucifer is going to snap his brother's neck. He tries to fight, but Lucifer literally says, "tsk, tsk" in his head and ignores Sam's struggles, pulling Dean's face down and kissing him lightly on the forehead. Dean pulls back, his face a picture of confusion.

"Our father is gone. I love my brother as much as you love yours. Perhaps all these years of abandonment have shown him to love me as much as Sam loves you."

"What?" There's a look of slowly dawning horror on Dean's face, but he hasn't quite caught on before Lucifer says one last thing.

"Close your eyes, Dean."

The second before the angel leaves, all the swirling alien emotions Sam has been feeling flash as bright as the wash of white light that blots out everything. Protectiveness, old anger, hate, regret, rejection, and so much love he finds himself falling to his knees off the bed. Which are suddenly his own knees again, and the vast presence of Lucifer is completely gone from his mind.

"Sam?" Dean asks, and Sam looks up to see his brother's face torn between fear and horror.

"It's me, Dean. He's gone."

Somehow, Dean's eyes get even wider. "Lucifer? He's been wearing you around?" At Sam's nod, Dean asks, "What the hell? How long?"

Sam doesn't really want to answer, so he prevaricates. "I guess we're not the only ones with serious brother issues. I think he went off to find Michael," at Dean's worried look, "but not to start the apocalypse."

A pause, and then Dean asks, scrutinizing Sam's face, "You okay? What do we do now?"

"We'll work it out. And I'm fine, better than. Right now, I know exactly what we should do."

And before Dean can say anything else, Sam screws up his courage and reaches for him. He still half-expects Dean to push him away when he pulls Dean close and matches lips, needing to finally experience the feel and taste of Dean's mouth for himself. Dean doesn't resist, and the kiss is sweet and lingering though he can almost feel the confusion and hesitation pouring off of Dean.

There's still a lot of questions in his head about Lucifer and the other angels and what the fallout for the rest of the world is going to be, and Sam knows the horsemen are out there somewhere. Right now, that's all things to be sorted out tomorrow. He and Dean have a lot of time lost to insecurities and doubt to make up for.