Disclaimer: I don't own Supernatural or its characters - these were created by Eric Kripke - I'm just borrowing them. I'm not making any commercial gain. No harm or infringement intended.
Sam is never alone, Luce is a constant presence and Sam likes it. Spoilers for season 7. Set after 7.04 'Defending your Life' and diverges from the series from then on.
This story runs parallel to, then follows, the events in 'No Way Home', so I'd encourage you to read that one first to get the most of this, but it's not essential. It's another dark one, I'm afraid.
~#~
... Resist the devil, and he will flee from you - James 4:7
Be alert and of sober mind. Your enemy the devil prowls around like a roaring lion looking for someone to devour - 1 Peter 5:8
~#~
The Devil on Your Shoulder
Dean has no idea what's going on. He's just glad to have his brother back and relieved that he seems none the worse for wear since the fall of the Great Wall of Sam. He either doesn't notice, or chooses to ignore, the moments when Sam's attention seems to drift, or the odd times he hears Sam laughing to himself, which more often than not is when he's alone in another room.
What Dean doesn't know is that Sam is never alone.
For a while Sam had followed Dean's advice to concentrate on what was real and resist what wasn't, and although exhausting, at first this had worked well. But after a while he'd grown complacent, after all he had managed 120 years in Hell, more than both his father and brother, and he was fine, he could cope, he didn't need saving.
Luce is now a constant presence; giggling, plotting, and whispering rude comments in his ear.
After a while Sam starts to quite like it.
Especially when Luce states categorically that it was Michael that tortured both of them while they were caged together in Hell. Although Luce made a compelling argument, Sam did make the mistake of voicing his initial skepticism of this version of events.
"Why on earth would I want to hurt my own vessel, after all the trouble you put me through to get you to say 'yes' to me in the first place?" Luce chuckled in disbelief, although this was at odds with his body language that seemed to say Hark at the stupid mud-monkey, and Sam found himself in the strange situation of feeling guilty for upsetting the Devil.
"Don't you project your human impatience on me, Sammy. You forget that it's me that was locked in the Cage for two-thousand years, before you jumped us both back in again," said Luce, for once sounding irritable with his vessel.
"Sorry. I'm sorry, okay?" Sam apologized, forgetting for once to complain about being called 'Sammy'. It had been a confusing time in the Cage, and in all honesty he didn't really remember very much about it. It was all an incomprehensible blur of excruciating pain, intense claustrophobia, and a sensation of something vast and terrible standing over him.
"Anyway, even if it hadn't been for you, do you really think that it would've taken me more than a couple of hundred years to get back out again, given the disarray that Heaven is now in?" Luce continued in a softer tone, having accepted the apology, but unable to resist putting in the metaphorical boot to his father.
Families have a tendency to bring out the worst in us, thought Sam, casting his mind back to all the arguments he'd had with his own father and the way that dealing with his dad had always left him feeling like a moody teenager again.
"Michael was always the petulant one. And a sore loser," Luce added, picking up on Sam's train of thought. They'd tried at first to stay out of each other's minds, but it was difficult when you shared the same head, and the dividing line between where Sam stopped and Luce started had become more than a little hazy in recent weeks.
"All his existence he'd been built up to believe that he was going to win the greatest prize-fight in history and get the keys to the Kingdom. And what happens? Not only doesn't he get the outfit he'd set his heart on, but then at the eleventh hour he gets pushed in a hole by some snot-nosed kid," laughed Luce, giving a cheeky wink to take the sting out of any insult.
It was like someone had switched a light on in Sam's mind. He realized that Luce had been the terrible thing that had been standing over him in Hell, and he hadn't been attacking him, he'd been trying to protect him.
Sam picked up on a feeling, a thread of anxiety, from his now constant companion.
"What?" he asked in surprise.
"I was only... protecting my assets," said Luce in defense, looking shiftier than normal.
Oh my God, he's trying to hide his feelings from me, thought Sam, stunned. Even Sam who liked to discuss everything from every angle and to the n-th degree wasn't quite ready to talk about this just yet.
"You keep your hands off my sweet ass...ets," said Sam, trying to defuse the tension with a lame joke, but instead the truth of it hung in the awkward silence between them.
Dean chose that moment to stumble into the room. His eyes were red-rimmed and bloodshot, underlined with dark purple marks - badges to the amount of alcohol that he was getting, and the quantity and quality of sleep that he wasn't.
Pushing past Sam who had tried to lay a comforting hand on his arm, Dean grabbed his jacket and keys and made to leave.
"Really? Are you quite sure you should be driving like this?" asked Sam, and even he winced at the strident tone to his voice.
"I'm fine Sam, jus' leave me be," slurred Dean.
"Wait," Sam insisted, laying a tender hand on Sean's shoulder, "I'm sorry, I didn't mean for it to sound like that. I'm just worried about you. I just... I just want you to know that I'm here for you, man."
Dean just stood there for a long moment just staring at Sam's hand. With a shock Sam realized that his hand was right over the handprint scar from where Cas had dragged Dean from Hell, and it was almost like a tiny crackle of energy was trying to push his hand away. That's new, he thought as he pushed against it harder, before realizing that what he was doing was more than a little insensitive.
"Sorry, sorry," he mumbled in embarrassment, dropping his hand in sudden shame.
"I hafta go," said Dean, he voice cracking as he all but ran to the door in his haste to get away.
Sam looked on in indecision, unsure if he should try to stop his brother or not.
"Let him go," said Luce, his eyes wide in surprise, "The boy needs his angel."
Sam narrowed his eyes as he looked at Luce, Maybe this is true.
~#~
No matter how bad it had been in the past, Sam was reassured that now his hallucinations were only the product of his own mind and not some diabolical, external influence trying to corrupt him.
Although that wasn't to say that he didn't have an occasional tendency to forget this sometimes, and he often found himself treating Luce like a real person, even more so in the last week or so.
In an odd way, he would have worried more if he hadn't been possessed by Lucifer in the past, as it meant he was familiar with the sense, almost like a taste, of his Satanic Majesty's presence, and there was something subtly different about Luce. Something more human and relatable - in many ways he was a more functional human being and a better companion that his own brother.
As if to prove that point, Dean came staggering back into the cabin a couple of hours after he'd left. He was soaked to the skin and shivering with cold, and fear, and unfamiliar emotions. Broken. God, was he broken. Sam had never seen him like this before and it was only the act of comforting his brother that stopped Sam from spinning apart himself.
Luce seemed to take this as a cue to step back, staying silent and keeping out of the way, although he hovered in the background always near to hand. Sam appreciated the comforting presence and being left free to do his best to comfort the walking wounded that was his brother.
Once Dean had confessed the true depth of his feelings for Castiel it wasn't long until he slipped into a deep, exhausted slumber. Sam sat at his brother's side keeping a close watch over him, fearful of what Dean might do in such a fragile state of mind, but he cast the occasional sideways look at Luce who was stood lost in thought and staring up out of the window at the stars.
Is Luce real or imaginary? thought Sam, now no longer quite so confident in the answer to this as he had been before. He thought about Luce's recent actions, and shook his head. Does it even really matter?
He did not notice the small smile that played across Luce's lips.
~#~
"Sam, wake up."
Sam jolted upright in his seat, disorientated and unaware of having fallen asleep. His eyes felt gritty and his head pounded from tiredness.
Luce was standing at his side, looking down at Dean - who seemed to be on the verge of gasping for breath - his expression grim.
Dean was fading. Fast.
Maybe from the weeks of not taking care of himself, maybe from last night's near drowning, or maybe even from a broken heart. Whatever the cause, Dean's skin was pale and clammy, veins bulging in his neck and his breathing was irregular and shallow.
They'd talked last night of taking Dean to hospital, rejecting the idea since they knew it would be swarming with Leviathans. Sam wondered now if they'd made the wrong choice.
Luce cupped Sam's cheek in his hand, making sure he caught eye-contact with the young man, so that there was no mistake in what he was about to say. "You need to say goodbye to him," he said in a sad, but firm voice.
Sam choked, he face twisting in disbelief, "No, this can't be happening, not after everything we've been through. He's sacrificed so much already, this isn't fair," he moaned.
He pushed away Luce's hand. "It isn't fair!" he screamed in rage.
"You're supposed to be an angel, isn't there anything you can do?" he begged in desperation.
"I'm fallen, Sammy and I'm not even really here, remember?"
Sam turned away in despair.
Luce gazed at him with soft eyes, "Wait, you do still have my blood in your veins, which means you should have some access to my power. If you let me guide you, we might be able to at least pull him back from the edge."
Sam wiped his eyes on his sleeve, "I'm not sure, do you think that'd work?" he asked in a small voice that would break all but the hardest of hearts. Like Luce's.
"Let me help you. You can trust me on this, have I ever lied to you?" he asked laying a warm hand on Sam's arm. Sam covered it with his own.
"No, you never have," Sam smiled.
Luce smirked to himself. When he'd walked the earth he'd once told Sam he would never lie to him. That had only been the first of his many deceptions. Poor Sam, he thinks he's so clever, and he's so arrogant that he can't believe he could be tricked. How naïve.
The thing was, he did love Sam. He loved the contradictions. He loved how pretty he was, those big soulful eyes Sam used for manipulating people into getting exactly what he wanted, and then if that failed how he used his large size and physical presence to intimidate those he couldn't peacefully coerce.
He loved how innocent and protected Sam was as the youngest and most cherished of his family. He looked forward to corrupting him, and watching it happen would make a delicious torture for his older brother. But for now he needed to bury those feelings down deep again so that Sam couldn't detect them.
~#~
The ingredients for Luce's ritual were all straightforward items that, as a hunter, Sam had close to hand. He winced as, under the fallen angel's directions, he carved a complex sigil into his own arm with a long silver dagger. Sam ground his teeth in pain as he squeezed the wound hard to collect a small half-glass of blood, while telling himself that anything was worth it, if it would only save his brother.
Finally the ritual was finished.
"Sammy, would you take that glass over to your brother?" asked Luce with a sly smile on his face.
Sam stood motionless, a look of confusion descending over his features, "I can't move," he explained.
"Good," answered Luce, picking up the glass of blood, carrying it over to the bed, and then pouring the entire contents into Dean's mouth. The demon blood quickly did its work of healing and changing the older Winchester.
Trapped inside his own body, Sam wailed in betrayal and fury, "How?"
Luce's recollections came quick and fast, how even in the Cage, Lucifer had still had some sway over Death – much to that entity's immense displeasure - and it hadn't taken much to have a seed of his fallen Grace planted in Sam's soul. That seed had then grown, protected from discovery behind the wall of Death's making, into Luce.
Sam saw how the plan had almost failed when Cas' subconscious had sensed that there was something wrong and the angel had felt compelled - against his better nature - to destroy the barrier in Sam's mind, but by then it had already been too late.
Luce was certain that Cas was still alive out there somewhere - the reaction of Dean's scar to Luce's presence in Sam seemed pretty conclusive - and now he'd corrupted the Winchesters, the former god-angel was next in his sights. Castiel would make an ideal lieutenant in his new fight against heaven, even if he didn't know it yet.
Luce snorted in amusement as he sensed Sam's feeling of hope at the thought of Cas still being alive, that somehow the angel would save him.
Don't bet on it, Sammy, he smiled, as he watched Dean wake, admiring the satanic beauty of the new black-in-black eyes of the older Winchester.
~#~