With Grace in Upswept Curve
Death gave Sam his soul back. Sam's body screamed in agony and his soul was so overwhelmed by physical sensation -- after a complete lack thereof in nearly two centuries -- that he shut down.
When he woke, his first thought was Dean. He went to see his brother, hugged him with all his might, and fought back tears of joy. That was the first time he noticed them. Dean's arms wrapped around his back, and something by Sam's shoulder blades twitched. Sam forgot all about it after a minute, getting caught up in puzzling out what had happened in the year (so much more than a year) that he'd been gone.
The second time he noticed them was in Bristol. After his flood of memories dragged him into a Hell flashback, he woke up and his shoulder blades burned. It felt like the muscles and tendons around them were all inflamed. He tried to look at his back in the mirror in the hotel room, but he couldn't see anything wrong...at least not when he looked at them directly. When he looked out of the corner of his eye though, he saw something -- something like light bleeding out of his skin. The feeling faded after a few hours and he forgot about it again.
The third time Sam noticed them was after they came back from visiting Samuel Colt. He went to take off his 'disguise' and felt the material pull on something. He saw a feather float to the floor and grabbed it, or at least he thought he did. When he looked again, there was nothing there.
The fourth time Sam noticed them was after Castiel wrecked all that was left of the wall in his mind. He woke up in the panic room, saw Dean's note and knew he had to get to him. He had to help Dean and Bobby stop Castiel. But it was far, it was so far, and he couldn't even see straight -- his vision was Hellfire-tinted and his body twitched and spasmed with every remembered slice, tear and lashing.
Sam stood and his legs nearly gave out on him. He leaned on the cot and bowed forward as an indescribable pain shot through his shoulders and down the sides of his back. He screamed and could've sworn he felt his skin tear. He didn't have time for this, he had to get to Dean now. He fought to open his eyes and concentrated on his goal. He tried to take a step forward and barely caught his balance when the floor beneath him just disappeared.
He heard the sound of wings beating, and his back undulated in the oddest way...and then he was somewhere else, standing on a street, near the Impala.
Something like that would be hard to forget under normal circumstances, but when a trusted friend, an angel goes power mad, declares himself God and demands everyone bow, well...that takes priority.
When Sam told Dean about seeing Lucifer (all the time) he hated how it made him feel. He knew he was seeing things, but telling Dean about it, saying it out loud, made it even more real. When he woke up one morning and found feathers all over his sheet, he held onto a handful of them, brought them downstairs and put them on the kitchen table in front of Dean.
"Where did these come from?" Sam asked, nodding at the feathers.
"Where did what come from, Sam?" Dean asked him.
Sam swallowed, bitterly, and walked back upstairs to shower. He ignored his reflection in the mirror, especially the sharp bones he thought he saw jutting out of his back, as well as the feathers that were growing thicker as he watched.
Sam didn't think of them again for a long time. He had to concentrate so hard to fight off his hallucinations already that a slightly off perception of his own body seemed like a paltry concern in comparison.
It wasn't until the leviathans came to finish them off while they were in the hospital, as Bobby lay dying, that he remembered them again.
More accurately, Lucifer reminded him of them. He sat at Sam's feet, cross-legged, saying, "Shame about Bobby." Lucifer smirked, adding, "If only someone here had the power to save him."
Sam ignored him.
"You're not even going to consider the possibility, Sam?" Lucifer shook his head and shifted his form from Nick to Sam, "Why do you think my wings are growing out of your back?"
Sam sat up as a chill ran down his spine. Lucifer was gone. Dean was in the same fugue state he'd been in since Bobby flatlined the first time.
Sam stood, shaking only slightly and walked over to Bobby. He shrugged his shoulders and felt the weight of heavy, enormous wings shifting. He'd been ignoring them, hoping they'd go away like every other hallucination, but now he understood. They were real, they were real, they were real.
Sam put his hand on Bobby's forehead, and spread his wings.
Dean stood up and saw Sam -- saw a light flaring out behind him -- two enormous wings made of pure light, as bright as the sun. He saw the light flow down through Sam's arm and into Bobby.
Then Bobby woke up.