Spoilers: 5x22 but ignores some plot points re: demon blood.
Notes: Written for hc_bingo using the prompt possession/mind control. See the full card here.
Summary: How Sam learned to stop worrying and love the devil possessing him.
Lucifer, as it turns out, is fond of honey.
Sam does not particularly enjoy it but he eats it on toast for Lucifer almost every morning all the same.
They've been together for about four months now. Four months since Sam said yes and changed everything.
At first, they fought for control. Lucifer wanted to search out Michael and complete what he saw as his destiny, wanted to remake the world and wipe humanity off the face of the Earth. Sam wanted to protect his family, protect his species, protect the world.
All in all, that first month was horrible for everyone.
Dean was constantly on edge, afraid Sam would lose the battle and Lucifer would resurface at any moment. Sam was relegated to Bobby's where the hunters and Castiel watched him every moment of the day.
Sam himself spent most of his time arguing with Lucifer, trying to make him see that mankind is made of more than just the sum of their faults. So, yes, he spent most of his time trying convince Lucifer, but he began to listen as well, to learn the devil's objections and history. And slowly, the desire to find Lucifer's weaknesses morphed into real interest about life before humans and Lucifer's family - and the devil was more than happy to hold Sam's attention.
Sam was stronger than the Angel had expected, wrestling control from him when Lucifer was distracted with the bloodshed of the demons he had called to give Sam his revenge.
In the end, Dean hadn't been able to watch his brother take that leap into Hell - had dragged Sam back from the edge and promised they would find another way. Sam just had to hold on to the devil. Keep him wrapped up tight until Cas or Bobby or someone figured this out.
Staying in control of his own body became easier after that - with his family supporting him despite the terrifying presence he housed.
Lucifer did not understand. He had been counting on fear to drive them apart, to have Sam all to himself, and instead he was trapped in Sam's mind, watching the humans rally together. Sam thinks that it was actually good for him. That seeing Dean, Bobby, and Cas accept and support him made the Angel ache for his own family. That Lucifer's preoccupation with Sam made him incapable of hating the humans who meant so much to his vessel.
For that first month, Sam was feeling more than a little claustrophobic. With Dean watching him constantly and Lucifer trying to convince him that the Apocalypse offered the Earth a new start, he thought he was going to lose his mind. But the longer he held onto to his control, the more relaxed everyone became.
Cas stopped staring at him like he was about to snap and kill them all and Dean started telling bullshit stories again, relaxing in the scrapyard with a beer (Sam still wasn't allowed to drink).
And Lucifer stopped trying to pressure him all the time, started listening to him. First out of boredom and then with genuine interest, learning everything about Sam that he was willing to share. He would be silent for long periods of time as Sam tried to show him examples of his childhood, where people came together, the best examples of humanity that Sam knows.
By the second month, Bobby started going back out on hunts, leaving Sam at his place with the company of Dean or Castiel. And soon after that, Cas started leaving for longer periods of time as well.
Dean was still hesitant to leave him alone but the extended inactivity was clearly grating on him.
It was bothering Sam as well. He spent long days lying on Bobby's couch, pretending to be reading while actually conversing with a petulant Lucifer. To Sam's surprise, Lucifer was more than willing to entertain him with stories. Sam learned more about Angels and Heaven from the devil than he ever had from Bobby's books.
His favourite stories all took place before humans evolved, when Lucifer's voice would take on a nostalgic tone and he would talk about his brothers, their discoveries and hijinks on the newly formed Earth.
Dean would still give him suspicious looks, but they were tinged now with an "I know what you're doing and I don't like it" eyebrow rather than the all-consuming fear that the devil is about to take over and smite him.
To Dean's relief, however, Sam and Lucifer's growing familiarity did not appear to damage Sam's ability to stay in control of his body.
They traded personal information and Sam found himself staring blankly at the television long into the nights, his attention focused inward. Lucifer was beginning to be a comfort to him and Sam found it rather ridiculous to complain about being confined to Bobby's when the Angel had been trapped in Hell for all those years.
Lucifer did not push outward anymore, became content to be united with his vessel, curled around Sam's soul and making the human feel strangely complete, like everything he had been searching for was finally found.
Things continued in much the same way until the second week of the third month when Sam thunked his coffee mug down on the kitchen table and refused to be babysat any longer.
And so he and Dean (and Lucifer) packed up and hit the road again. They didn't talk much about Sam's passenger and if Dean noticed that his brother's reflexes were a little quicker, or that his temper was a little wilder, then he didn't mention that either.
Sam asked Lucifer about those changes one night as Dean slept and he and the devil rested metaphysically against one another.
All of my powers remain intact, Sam, Lucifer had answered him in amusement.
Lucifer's emotions came to him in flashes, brief insights that felt as real as his own.
Really? Sam was surprised to hear that since he had not thought himself capable of any of things Cas could do, let alone use the powers of an Archangel.
I keep them from you, Lucifer admitted after a long moment of silence. Sam could feel the uncomfortable prickle of guilt in the press of the Angel's Grace and he could not stop his own flare of hurt at the revelation.
Although to be fair, Sam was not exactly allowing Lucifer use of their body. It seemed to him as if Lucifer could not stop leaking his Grace and abilities into his vessel, though, because Sam had noticed an increase in his physical power and quickness since joining with Lucifer. It looked to him as if the balance of power between them was extremely one-sided and that bothered Sam more than he wanted to admit.
It seemed that way, but Sam would soon find himself mistaken as they all eased into the new routine of hunting with an Angelic presence inside Sam's head.
The first time Sam lost control he almost didn't even notice.
It happened just after a hunt. He and Dean were driving back to their motel and Dean was trying to be as obnoxious as possible, attempting to annoy Lucifer and Sam by blasting a Christian rock station on the radio. Sam was even more pissed about it because he knew Dean was clearly ready to make himself suffer just to irritate them.
Sam was complaining – loudly – and just about to throw Dean one of his best unimpressed looks when his hand moved to the center console and deftly turned the entire radio off.
The ensuing silence was the loudest he had ever heard and it slowly dawned on Sam that the action was not his. Lucifer was also conspicuously silent and he was still enough that Sam began to wonder if he hadn't imagined it.
He didn't bring it up, just pushed the incident to the back of his mind and promised himself that if happened again he would tell Dean. Sam did wonder, however, why Lucifer was not confirming or denying his suspicions, especially seeing how impossible it was to hide thoughts and emotions from each other.
The second time it happened, Sam was making a sandwich.
Lucifer had begun to experience the world of food and drink through their shared senses and was not shy in letting his preferences be known. The first time Sam had eggs after being possessed, Lucifer was so disgusted that he spent the following two days telling Sam in painful detail what he had done in order to create demons. It was scarring enough that Sam eventually promised that he would never eat eggs again so long as Lucifer kept those details to himself.
He also expressed a distaste for mustard. A distaste that Sam, on this particular occasion, had forgotten about completely
Sam was just shaking up the bottle of mustard to finish his sandwich when, without warning, he was throwing the whole thing across the kitchenette. The bottle hit the room's window, the cap came undone with the force of it, and the mustard spilled all over the already stained carpet.
For a moment, he just stood in stunned silence.
I hate mustard.
There was no denying it any longer: Lucifer was learning how to bypass whatever wall Sam thought he had up.
After the mustard incident these moments began to happen more and more frequently. Sam would find his left hand throwing a knife into the throat of a demon that had snuck up behind him or would find himself tossing a weapon to Dean before his brother could finish asking for it.
It got to the point where he had to sit Dean down and explain. Predictably, it didn't go well.
Dean, to put it mildly, freaked. He refused to see that Lucifer hadn't actually done anything, hadn't used his Angel mojo to kill everyone, or shoved Sam's consciousness aside, or even made any snide remarks. So far, anyway, all he had done was help. And throw mustard across the room.
Dean's disapproval notwithstanding, Lucifer was rapidly overcoming his former helplessness. And Sam was rapidly learning that he didn't mind. After many false starts, sullen silences from one or the both of them, and pounding headaches, Lucifer and Sam finally managed to find an awkward sort of rhythm together.
Their long conversations continued during the hours that Dean slept and Lucifer began to allow Sam access to his abilities. They fought spectacularly well with the addition of Lucifer's Grace and Sam's instincts and even if Dean didn't trust it, he had to admit that their success rate was climbing.
It progressed to the point where Sam was not only comfortable with the devil, but actively craved him; until he was pleased to have Lucifer stroke them to orgasm most nights, introducing the devil to a new human sensation and a reason stay. Sam tried not to think about how it must be the most screwed up relationship in history, how it barely even qualified as a relationship at all.
By the end of the third month Sam was no longer certain why he had been so terrified of being Lucifer's vessel. They just fit together.
Like we were made for this, Lucifer would insist whenever the thought crossed Sam's mind.
And it was true, Sam had never felt more at ease in his life. Lucifer kept them hidden from Michael and the Host and was even lending a hand tracking down the last Horsemen. Sam could feel how much of a big deal that was for him, admitting that his destiny – perhaps – lay with one otherwise insignificant human soul and not in revenge.
Castiel would pop in now and then, report that they had no idea what was going on with Lucifer's disappearance upstairs. He would come with updates on his new quest to separate Sam and Lucifer but by this time the thought of living without that presence in his head, wrapped around his soul, scared Sam more than anything else.
Dean would not accept this new development until the accident.
It happened out of the blue. Sam had been gassing up the Impala while Lucifer was curled in the back of his mind, as close to being asleep as possible for Angels. The demons hadn't even known who they were attacking, they were just scared and driven from their usual haunts by searching Angels.
It took no great effort for Sam to dispatch them but the result was rather bloody and he had become used to relying on Lucifer's strength. The pull of the blood was too much and all it took was one accidental arterial spray to catch his lips and Sam was lost to it.
Lucifer pulled him out of it, but it was much too late. The demon blood coursed through their veins, amplifying their strength and power but also lending them an animalistic need to destroy. In the part of his mind not mad with power, Sam panicked. The high of demon blood was not worth the pain of withdrawal and he was disgusted with himself for disappointing his brother.
With Sam more easily overcome by the fierce desires inspired by the blood, it was Lucifer who finally got them under control and back to their current motel room.
There was no hiding it from Dean, their eyes had gone completely black and the excess power was crackling around them.
Sam doesn't remember much of what happened in the next day or so. From what Lucifer and Dean tell him, the devil had kept him securely hidden away and had borne the brunt of the physical withdrawal. Sam was spared having the hallucinations, the out of control pulse and fever, the muscle spasms and inexplicable psychic surges. And it was that act, Lucifer's willingness to suffer for Sam, that finally brought Dean around.
It was like waking from a deep sleep when Lucifer finally released his death grip on him. The first thing he felt was the Angel's unwavering concern – it was only after that Sam registered the muscle aches and weakness, the way their throat was scratched raw as if from screaming.
They recovered quickly thanks to Lucifer's healing Grace but Dean never looked at them the same way again. Even when they were obviously two people despite the single body – when both of them were writing notes for a case or when Lucifer would interrupt Sam because what he has to say is more important - even then, Dean's gaze held a sort of grudging respect. A love for his brother, of course, but also a growing appreciation for the Angel sharing his form.
And so now, as their fourth month together draws to a close, Sam is finally feeling at peace with himself and his place in the world. Lucifer is as calm as he can be while constantly bombarded with humanity, and Dean has even stopped making off-colour “you have the devil in you” jokes.
They still have to ice Death and convince Michael to back off, but with Lucifer on their side both Winchesters are starting to believe that they actually have a fighting chance. And as long as he gets his honey every morning and Sam keeps mustard far away from them, Lucifer seems content with this life as well.
Castiel still drops in occasionally but he is not yet taking the devil's current residence as permanent thing. It hurts Sam that his friend is so convinced that that is all they are, a mere vessel and an Angel instead of something destined, but he is not giving up hope that he can get Cas to come around.
And in the meantime, if Castiel does find some way of prying Lucifer away from him against his will, well, Sam is going to fight against it just as hard as Lucifer himself. From the way that Dean scratches the back of his neck and looks sheepish whenever Cas talks about requiring his help in order to separate them, Sam thinks that he has an ally in his brother, as well.
The only thing that Sam is dreading right now – more than Death and Michael and ever-present fear of having Lucifer separate from him – is breaking the news to Bobby. Dean has wisely backed out of the situation, telling Sam in no uncertain terms that this is not his battle.
Lucifer laughs at his nervousness but Sam assures him that the elder hunter is not going to take the news that the man he sees as his son is in a pseudo-romantic relationship with the Prince of Lies while they share one body as a good thing.
Oh, God, Sam thinks to Lucifer, Forget Michael, Bobby is going to kill us all.