It was gross and icky and disgusting. Sam wasn’t sure why he felt like he had a body inside his- Lucifer’s, now- brain, but he knew that his senses were telling him he was trying to vomit and couldn’t around the gag Lucifer had shoved in his mouth when he was done talking him into torturing demons. It was a mess.
When he’d let Lucifer in, Sam had thought that he’d have a chance. He thought that in his own mind and body he’d have some extra power against Lucifer to even the playing field. He couldn’t have been more wrong. If Lucifer was an unstoppable monster on the surface, he was ten times more powerful and horrible when he was inside Sam’s mind. He should never have said yes.
The darkness was everywhere. And then it hardened and condensed into a form, and Lucifer was there, roughly pulling Sam forward. He didn’t look like a vessel there in Sam’s mind. He looked like himself, and he was horrible. He was- the loveliest, most beautiful thing Sam had ever seen. He wasn’t something Sam could’ve imagined in his wildest dreams. And he fit perfectly with Sam. All of that just made the twisted, ugly, sick distortion of his face more awful. Because as terrifyingly evil as he was, he was still far more beautiful than anything.
Lucifer dragged Sam to a place in his mind where he could see out his eyes. There was a field. And- Dean! Dean was there! Sam made a desperate grab towards the image, but he couldn’t escape from Lucifer.
“I brought you here to watch,” Lucifer purred, voice gentle. His words were musical, in a way. They reminded Sam of the most haunting pieces of Rachmaninov’s Isle of the Dead. “Watch as everything you’ve worked for and sacrificed for falls apart. You knew this would happen. Why do you always fight so hard?”
Sam growled at him, muffled by the gag. He tried to hit Lucifer, but Lucifer caught his arm gently and held it down. He stroked the pad of his thumb along Sam’s cheek in a way that was distinctly creepy. Sam whimpered fearfully. Lucifer couldn’t want that, right? He choked back a sob and tried to get his anger back.
Through the eyes that used to be his, Sam watched Castiel throw a holy oil molotov at Michael. Michael went up in flames and disappeared. Sam didn’t honestly care about that, but next to him he could feel Lucifer’s rage. It was like the build up for a storm. The oppressive, dark calm made Sam choke.
He wasn’t surprised when Castiel exploded in a blur of blood and guts and shreds of bone. He just wished it hadn’t been his hand that snapped. Well, not his hand. Lucifer’s. His body and mind both belonged entirely to Lucifer, and all he had left to cling to was his heart and his soul. A weak, rebellious heart that couldn’t care about the world and watched the monster beside him with awe bordering on worship, and a tarnished soul steeped in demonic power. Sam was nothing.
Dean was talking. “Sammy? Can you hear me?”
Lucifer turned Sam’s- Lucifer’s- body to face Dean. He was angry. His posture was predatory. Unwelcome arousal built in Sam’s groin. That was Dean Lucifer was threatening! This was not the time to decide that Lucifer being angry was, well, hot. And he was still so horrifying. How could Sam think sexually about someone so icky and twisted? What was wrong with him?!
“Y’know, I’ve tried to be nice. For Sammy’s sake,” Lucifer told Dean with what used to be Sam’s voice. He reached forward, grasping the collar of Dean’s jacket. “But you are such a pain in my ass.” His movements were smooth, controlled. It was terrifying. He threw Dean backwards into the Impala, cracking the window.
Dean grunted in pain and struggled to get up.
A gun fired behind them, and horrible pain burned in Sam’s shoulder. He dropped to the floor, sobbing and screaming into his gag as his body convulsed. Lucifer seemed unaffected. Sam wondered dizzily why that was.
Sam’s- Lucifer’s- whoever’s body turned around just in time for another bullet to hit Lucifer in the chest. More pain exploded in Sam’s body. His vision went out, and he didn’t know what happened in the outer world. In their mind, Lucifer knelt next to Sam and pressed his hands to the wounds, instantly healing them. Sam thrashed and sniffled in shock.
“Nnnnghn,” Sam whined, “Mmph.”
Lucifer pulled Sam gently up into a sitting position and wiped away his tears. “Whoa, Sammy, it’s ok,” he cooed, pressing a soft kiss to Sam’s forehead, “It’s just the Colt. Hurts, but nothing we can’t fix. You’re ok.”
Sam scowled at him. Where did he get off fussing over Sam and kissing his forehead like they were friends or even lovers? They were enemies. They hated each other. Sam wished. He squirmed away from Lucifer and looked over at the window. Blood dripped from Dean’s lips as he stood before Sam, no, Lucifer.
“Are you in there?” Sam could see Dean was scared. He should be. He was facing down an archangel who was currently pretty mad at Sam, and Sam was Dean’s only hope of not getting beaten to death by said archangel.
Sam’s- Lucifer’s- lips curled upward. “Oh, he’s in there alright.” He punched Dean in the face, making Dean stagger sideways. “And he’s gonna feel the snap of your bones!” He knocked Dean to the ground with another blow. “Every single one.”
Sam caught at the Lucifer in his head’s hand, but Lucifer jerked it away. Sam whimpered miserably. There was no way out of this one. He’d have to find another way. But the pain of watching his own- no wait, Lucifer’s- fists beat his brother bloody was so distracting. There was nothing Sam could do but watch in paralyzed horror.
And it hurt so much. Hurting Dean was always the best and the easiest way to hurt Sam. To be forced to watch from so close, from the point of view of Dean’s attacker, helpless and with no chance of stopping it- Sam couldn’t do this. He screamed into his gag. He wished he could faint so he wouldn't have to witness this. He felt like every blow was his fault. And he knew that Lucifer’s anger wouldn't give out until Dean was dead. He was going to have to watch his own hands murder his brother.
Sobs tore from Sam’s throat, and he let himself collapse. Dean was dying. Sam was possessed by the most evil, horrible monster in existence. In a few minutes Michael would be back and he and Lucifer would destroy the world and millions of innocent people would die. And it would be Sam’s fault for saying yes.