Written for comment_fic on livejournal, a multi-fandom prompt community.
Prompt was Sam/Dean, The Goose Girl (for fairytale prompt day)
It begins when Sam says he is sick of doing what Dean says. That Sam is going to be the king of hell, and that Dean should just deal.
That went over about as well as you'd think it would.
Because Dean knew that he would fight for Sammy, even if the one he was fighting was Sammy himself. Dean had the memory his mother's love and his father's rules; these were the things that made Dean know exactly who he was, and this knowledge was his strength.
But as Sam grew more powerful, he began to employ more devious things, to use cleverness and spellcraft where shows of power had failed. He had some hell-allied witches take Dean's memories. As a clueless Dean stood before him, Sam maaged to convince Dean that he was Sam's younger brother, that he was the only thing he had left in the world. And that Dean had always listened to Sam, had allowed Sam to watch out for him the best way he knew how. And that their parents had always wanted for Prince Sam to protect Dean, to share with Dean all the spoils of hell with none of the risks. And in exchange, their last wish was for Dean to obey Sam. Always and with everything.
Dean hadn't wanted to believe it. But there was no denying that he and Sam had a strong connection. Even without memory, he could feel it. So he believed Sam.
So Dean obeyed. By day, he watched over a small safe patch of hell, where goose-demons roamed and ate the livers of chained souls. At night, he kneeled naked at the feet of Prince Sam's bed and did whatever he was told.
One night, when Sam was asleep, tired from his rough escapades with Dean, Dean snuck into the prince's bath chambers. He was desperate to feel clean, and as he stepped in the bathtub he felt a moment of relief, as he plunged in to the only cool, clear thing in all of hell. But his injuries from his time with Sam still made him wince, and as three drops of blood fell from Dean's body onto the marble ledge, Dean could swear that they spoke to him. They cried, "If your father only knew, his heart would surely break in two." Dean didn't remember his father. But somehow he felt that the drops of blood knew more of truth than he did.
The next day, as Dean sat over his tiny peaceful corner of hell, cleaning his favorite gun again and again - no reason, just to make it shiny -- Dean heard the goose demons talking about the prince's car. Curious, he went to the meadow where they had told him it lay, and he ran to it as soon as he saw it. Dean somehow recognized it as an Impala, and he slid into its front seat and starting caressing the dashboard. He started it talking to it, as well, until one of the nearby demons got concerned and told Sam.
Sam's nostrils flared and his muscles tensed when he saw Dean with the Impala, looking so much like the old Dean that it scared him. He immediately had the car destroyed, ordering that only the hubcaps would be spared, so that they could decorate his bedroom. Dean sobbed and begged, for reasons he himself could not understand, but then, as always, had to accede to Sam's wishes. That night, as Sam took him more viciously, more urgently - with more CLAIM - than he had since Dean first came to live here, Dean stared up in tears at the hubcaps. They sparkled briefly as they voiced, "If your father only knew, his heart would surely break in two."
The next day, Dean kept thinking about these things as he sat polishing his gun, watching demon geese. He was so distracted he barely noticed the explosions and shrieks and bright, bright lights until they were practically on him. And then he felt two hands, two burning but comforting hands, gripping him tightly.
"I am here to rescue you, Dean Winchester," the man said, eyes staring at Dean with both confidence and compassion.
Dean wanted to hold onto this man tightly, to let him take him wherever he might go as long as it was far far away. But Dean instead let a single tear fall down his face as he answered, "I cannot go with you. I must obey my brother Sam."
He looked at Dean with curiosity and then said, "My name is Castiel. You must come with me Dean." Dean thought he saw Cas distracted momentarily by the goose demons, and maybe even lick his lips a little, but Dean was sure he was just imagining it.
"I can't leave my brother."
"Then tell him to join us," Cas said, "Tell him to give up evil or be condemned forever."
"I can't do that," Dean cried in confusion, "Nobody can tell Sam what to do."
Cas looked at him again curiously. He gently touched a finger to Dean's forehead and waited for Dean's memory - Dean's identity - to flow back into him.
The change in Dean's facial expression was immediate as he suddenly understood all that Sam had done. The demon geese all flew away in a hastily formed vee when they heard Dean yell, "That. Little. Bitch!"
"Sam! Sammy!" Dean yelled as he stormed into the palace. He quickly walked up to Sam and punched him in the jaw.
"You got your memories back," Sam acknowledged calmly, with narrowed eyes.
Dean punched him again.
But Sam telekinetically threw Dean against the wall then, silenceing the murmurs of the demons who were starting to wonder if the prince's consort might be challenging the throne.
Cas, however, pushed aside the minions and quickly placed his hand on Sam's face. He said, "Now that your brother knows what you do, he surely won't let go of you. Now you are one, which once was two."
And with that, Sam was bound to Dean, more tightly and irrevocably than he ever was as a brother or prince. And when Cas grabbed Dean tightly and raised him back to earth, Sam's soul had no choice but to be pulled along with it.
And after much arguing and punching and namecalling, and a few near misses with the end of the world, the three of them eventually came to terms with the fact that spells and powers couldn't separate them. And so they eventually fought and found their way into a shared life, where each one knew exactly who he was, but were able to live with one another anyway.
And many years later, after Cas finally found a way to bring the Impala back to Dean, by killing the demon geese that were using its scattered parts for nests, Dean really and truly forgave Sam.
And then they all lived happily ever after. Except for the goose demons, which Cas cooked and ate for dinner.