'Till the Very End
It had been years since the angel had fought beside the Winchester boys; decades even. Castiel still held onto the same vessel as if it was a piece of their adventures. As you would've guessed, the two men died. I won't say if it was of old age, bad luck, or by a monster. I'm not really one for spoilers.
Early on, Castiel admitted to Dean that he would be with the Winchesters 'till the very end. He is a celestial being who is forced by nothing other than time to live in the days without Sam and Dean. Nowadays, he visits Heaven, roams the Earth, and does what he can to help the little, fragile humans. He likes to think Dean would be proud of him. He would be proud of Castiel saving people.
In his vessel, he walks the roads and trails with heavy stories being dragged behind him. Before he flew upon the Earth, the only knowledge he possessed was of obedience and being a foot soldier of Heaven. Then, he gripped Dean Winchester's soul tight and raised him from perdition. Then, and only then, did the angel learn something knew from the "puny" humans.
…
Castiel was standing outside of a dark warehouse, ready to complete one of his small missions. It was dark and only dim, orange, street lights lit the world. The mist was beginning to settle upon the angel's over coat. Castiel was about to walk inside when he heard an unfamiliar voice.
"Castiel? The Castiel?"
He turned around and saw a young man with brown hair and brown eyes in a cheap suit. It was another angel wearing a boy's vessel. Castiel tilted his head and squint his eyes.
Confused, he asked, "Who are you?"
"I-I'm Nathaniel. I'm a big fan of yours" he excitedly walked toward Cas and outstretched his hand. Castiel looked around him to see if there was anyone else with an explanation. He slowly shook the other angel's hand, still baffled.
"How did you find me?" Cas asked, worried that others knew of his location.
"Well, I'll admit it was very difficult trying to track you down. I asked around in Heaven which led me to Wisconsin, then Colorado, then-"
Castiel waved, dismissing the rest of the answer. "Never mind. You need to go. I must carry on with my work" He began walking away, but couldn't escape Nathanial for he was walking after him.
He came up on Castiel's side and said; "I know, I'm sorry, but I would love to work with you" The other angel rolled his eyes and walked a little faster.
"I work much better on my own" Cas replied, trying to be kind.
Nathaniel picked up his pace and added, "I would just learn so much from you. I mean, you ended the apocalypse, stopped the Leviathan, got us all back home to Heaven, and showed all the angels free will" Castiel stopped and looked at the eager angel.
He asked, "You do know I caused almost all of those things, correct?"
"Well, yes, but you cleaned up your mess. You fixed your mistakes. Not many other angels I know do that" Cas stood there in silence for just a small moment and appreciated his open mind.
A small smile spread across his face as he said, "Thank you, Nathaniel, but you should go back home; back to Heaven"
The other angel glanced down at his black dress shoes and added, "I don't want to go back and fill out paper work. I want to do something important like you. You were even in the Winchester Gospel"
Winchester
Castiel hadn't heard that name in decades, centuries even. He looked back into his past and saw those memories covered in dust. From time to time he would revisit those years. Whenever he saw just the right shade of green forged in nature, he thought of Dean's eyes. The occasional dog would even remind him of Sam and his puppy dog look. On a dark day in the past, Sam and Dean did pass into the afterlife; Heaven or Hell I won't say. Like I said, I'm not one for spoilers. They thought they would easily be forgotten, but over time they morphed into legends and stories of heroes. The Winchester Gospel is the texts of Sam and Dean's story, including Castiel's.
"Um, Castiel? Castiel?" the other angel pulled him out of his of reawaken thoughts.
"Oh, I apologize, Nathaniel…but none of those achievements were ever truly mine. I was only part of Team Free Will. Or at least that was what Dean used to call it. It was really him and Sam. I had pulled them both out of the fire and they did the same for me. I had seen them both go through so much turmoil and pain, yet they carried on. Sam and Dean Winchester never gave up, even at the very end. At times, the solution seemed nonexistent, but one of them would always believe there was a way"
He paused.
"Don't try to be like me, Nathaniel. Be like them"
Castiel met the young man's eyes.
"I try to"
The angel with wrinkles beneath his eyes and a weary mind walked off into the dark and misty night without another word. He left Nathaniel behind him to be alone with his thoughts.
The Winchester family, every single member, would be locked away in a part of the angel's mind. No matter how long he flies around Earth, Heaven, and Hell, they will never be forgotten. They will always be there; in his memories and in his heart.
Castiel had been and will be asked of Sam and Dean and their "adventures", and he will say the same type of things. He would tell the stories of worn leather, the faint smell of beer, rusted metal, and classic rock. Cas would tell those who wondered about the two boys who carried the heaviest of burdens. He would talk of the brothers who saved the world more than what was required of them, and had lost too many people along the way. Castiel, angel of the Lord, would tell the stories of the Wayward Sons.