Warning: Mentions of Hell, and technical gay stuff. This includes one-sided Destiel, which I do ship, but there's nothing explicit. I hope you enjoy.
Before Castiel rose Dean from Perdition, he had never talked with a human. It was considered a fast track to falling, and at the time, the thought of it scared him, so he stayed away from humans, simply watched from afar as their lives passed them by. But one night, he saw a house catch fire. He knew it was caused by demonic influence, so he went to help, but Zachariah kept him from going, so he watched, a feeling of dread creeping up his spine when he watched a child carry out an infant, and heard their father curse Heaven for letting his wife die. He asked why he wasn't allowed to help, but he couldn't remember getting an answer, or really anything for a long while. He was sent to see someone he doesn't remember, and he suddenly realised why he stopped asking questions. Then, it must've been 23 years after that house burned down (he never understood why it stuck with him after all this time), it was said the Righteous Man was in Hell. He had been in Hell for 10 years already, and he wanted to ask why they were only helping now, but he kept it to himself. He flew as fast as he could and fought harder than he thought possible, so that he would be the one to save Dean Winchester. He didn't know the Righteous Man's identity before he entered the Pit, but as soon as he smelled the first hints of brimstone and burning flesh, the name rushed into his mind. He didn't tell this to his Garrison, simply kept the knowledge to himself. As I was saying, he flew faster than the other angels, because he knew exactly where to go on a base level. "I'm going to save the Righteous Man." He remembered thinking. He was going to stop the Apocalypse from happening. It turns out he was too late. Dean Winchester had hopped off the rack while he was fighting, and had been off for 10 years. He didn't stop anything, and yet when he locked eyes with the blonde man, it didn't seem to matter. He repented, he didn't want to hurt those people, even if some were deserving, he didn't like hurting them. His soul was scarred, yet it was still vibrant. There was hope. He rushed towards him, hoping his light would soothe the man, and it did. Too bad he didn't see Alistair until it was too late. He clipped one of his lower wings, very small, yet very useful to a Seraph, and extremely sensitive to the slightest graze. He fell in his pain, body locking for what felt like a second. The Righteous Man watched, horrified, as the angel fell, brimstone and blood staining his graying wings. The wings that should be white, like his brothers that he saw get shot from the fiery sky, but were instead growing darker. Alistair laughed at Castiel's pain (and how did Dean know the angel's name anyway? It's like he saw him and just knew. How weird). "Poor little angel, trying to take my favorite toy away. I'll have fun tearing you to shreds." The angel didn't appear to be listening, standing in front of Dean in a defensive pose. "I will not let you harm Dean Winchester any longer." A few of his still white feathers fluttered to the floor at those words, while others grew greyer. Dean thought they looked prettier black than white; they matched his borrowed hair and bright blue eyes better than they would've if they were white. This time Alistair cackled. "Why do you care? You're too late." Castiel snarled. "I don't care! I will keep him out of your clutches if it costs me my life!" He didn't know where this need to protect came from, but he didn't pay it any mind. He could see more of his siblings arriving. He just might be able to save him. Alistair seemed to notice this too, and growled low in his throat. "Oh well, I guess I'll just have to settle for killing you later. You'd be wise to watch your back little angel." He disappeared in a cloud of sulfur, and the angel turned to the human, grabbing his shoulder tightly. He lightly pressed his fingertips to Dean's forehead, and the hunter fell into his arms, peacefully resting. He raised his wings high, spreading them out wide in pride, and shouted with all his might, "DEAN WINCHESTER HAS BEEN SAVED!" He took flight after his siblings then, basking in the wonderful feeling of holding the human close to his chest. He would never let that human go. And he did not. He stayed by Dean's side throughout the Apocalypse, and even fell to stay by the human's side. After a stressful hunt (fuck Wendigos, they were too messy), he decided to let his wings out (in his own motel room mind you, he would never let Sam see his wings). He reverently trailed his fingers down the black feathers, noticing how, in his opinion, they looked much better than they had white. They still had their elegant arches Seraphs are known for, but instead of 6, he had 5. He could still remember the horrible pain that came from Alistair cutting it off with expertise. He felt his second largest set, and how many of the feathers had a burned texture, and the uncomfortable heat of hellfire burning against them. He felt his largest pair, and how perfect they were, except for the blackness that signified an angel's fall. He supposed he had been falling since that horrible day so long ago, when 4 year old Dean Winchester carried his brother out of his burning house. He smiled suddenly. "I know you're there Dean, you may enter if you wish." The door creaked open before quickly shutting, and he heard footsteps near the bed he was sitting on. He turned to face the hunter (and secret love of his eternal life). "What is it?" Dean shrugged and sat beside him. "Sam's gone, and I'm bored. Figured you wouldn't mind some company." He glanced at the wings for a second before looking away, and Castiel held in a chuckle. "You may touch them if you wish, although don't be rough." Dean's eyes widened, before he gave a jerky nod and slowly, hesitantly, brushed against the feathers with his fingertips. The angel sighed and relaxed into the touch, his wings lifting ever so slightly to show he enjoyed it. As Castiel allowed his friend to groom his wings, uncaring (and actually appreciating) their dark color, he felt that, once again, he was grateful that he left Heaven behind, and he wouldn't change this path for anything, even the world. And if that was selfish of him, he felt he deserved to be selfish, if only with Dean.