Works as an "On the Head of a Pin" coda. Vaguely slashy overtones if you're so inclined. Otherwise it's gen.
Castiel likes to watch Dean Winchester sleep.
It started out as curiosity- Dean was, as far as he knew, their best chance of averting the apocalypse. He wanted to learn more about Heaven's newest weapon, forged in the fires of Hell. He isn't sure when that changed, but he knows that it has.
It is not that obsession itself is new to Castiel. Angels are, by their very nature, fanatical. Since creation, Castiel has done his work with the surety of the divinely inspired. There was never a question, no fear, no doubt, because everything he did was His will, and was therefore infallible.
Under His instruction, Castiel and his brethren laid siege to Hell to rescue Dean, and then...
Anna said what he's feeling is doubt, but doubt really only scratched the surface. Anna, who took the opportunity to know Dean before she recovered her Grace, and Castiel is fairly certain that the rush that goes through him at the thought is jealousy.
The real problem is that when it comes to Dean, Castiel wants, and after the battle of the blinding holy light against the darkest evil that has made up his world for millennia, the tangled grey web of desire threatens to overwhelm him at every turn.
It is a shade of love, Castiel recognizes that much, because he has felt Divine love. This love, however, is but the palest reflection of that-base, tainted and selfish. Because he knew when he pulled Dean out what Dean's fate was. What Dean would have to do. But try as he might, he cannot remain unaffected by the vulnerability he sees in Dean's eyes. All the self-loathing, hurt and accusation there flays Castiel with an intensity he did not think possible.
There are times when all he wants to do is snatch Dean away as he did once before. Away from the increasing darkness of Sam's soul that Dean still feels responsible for. Away from the nightmares and memories of Hell and the promise of a battle that might very well be the final one. He wants to take Dean where Heaven and Hell can't find them and wrap him in the soft cocoon of his wings, kiss the salt of his tears from his eyes and hold him until he knows some measure of peace.
Castiel knows, perhaps better than anyone, that no such place exists. And again he wants, so much that he thinks he understands how a drowning man feels. Not for the first time, he wonders if this is His will, if somehow it is imperative that Castiel understand what a precious thing is humanity, or if with every passing moment he is failing his most important test.
But his wondering doesn't turn up any answers, and when Dean asks another one of his endless questions, all he can offer is the truth as he knows it. There is no comfort to be found in anything passed down to Castiel from his superiors. There is not even the hope of comfort. There is every chance that Castiel wouldn't know how to give it if there were-another newly discovered drawback to his existence of absolutes. None of this keeps him from wanting to try.
"I promise," Castiel whispers to Dean's sleeping form, "I promise, whatever may come, I will do everything that is in my power to keep you safe. Whatever it takes. I swear."
He has his orders, and this is not a promise he is sanctioned to give. It is not a promise he has permission to keep.
And yet, there is a blissful release as the words leave his lips. Castiel finally knows the terrifying feeling of choosing his own course of action.