The One Who Forgave Angels
Angels could see the future.
Every hundred years, they were given a vision of themselves and what they would be doing in one hundred years' time. Castiel usually saw himself watching humanity, and once he had predicted a battle with a demon horde, but nothing unusual.
This year was different. There were so many angels that it took one hundred years for them to all go through their visions, and when one finished the angel created after immediately started seeing their future. It was only a short viewing, ten minutes at most.
Anael was concerned by what she had seen. She hadn't shared it with Castiel, but he could tell it worried her. Uriel and the rest of the garrison had their visions after Castiel did, since he was second in command of their garrison. A day after Anael had her vision, Castiel experienced his.
As his turn came, he thought he would see the usual. Watching over humanity. Instead he saw something very different. Himself, in a vessel, naked, twisting and moaning underneath the hands of another man, someone with brilliant green eyes and a soul that burned hotter than Grace.
He was also concerned about this, and when Uriel had his, as well as the rest of their garrison, they were all silent. Usually this was a time for sharing, but no one wanted to share what they had seen.
Sariel finally told him, in hushed whispers, that everyone in the garrison had dreamt the same thing. Darkness. They all knew what that meant. Castiel nodded along, even though he himself had not experienced the Darkness.
He asked Anael if she too had seen the darkness. She had nodded in reply, but had said to him, "But you did not."
Castiel would have blushed if he had been in a human vessel. Anael had always seen into him in ways that the others could not.
"No. I did not see the blackness."
"Then what did you see Castiel?" Anael asked. Castiel was silent at this, and Anael did not push the question. It made him pitifully glad.
When they are called to rescue the Righteous Man from hell, Castiel sees on his siblings faces that they know that some of them would not make it out alive. Still they went, and some died, but not all.
But when Castiel went to greet the Righteous Man, with his own brand upon his shoulder, he found himself speechless for the first time in his existence.
It was him, the green eyed man with the soul of fire, who he had seen in his vision. And all throughout all of his interactions with the human, Castiel kept this knowledge in his mind, also knowing that the hundred year period was only four years off passing. He would wait that long.
His fall from Grace disillusioned him, but Dean once again proved him wrong, being there and showing him the sun was still shining when he came out of himself. And he proved that Castiel had been right, all those years ago, when he had that vision, as the one hundred year date passes and he is losing himself under Dean for the first time, his faith in his Father and siblings shattered, but maybe, just maybe, rebuilt in this man. The one who forgave angels, even though all of his sins should have turned Dean from him long ago.
And when they are finished, and Dean has dropped off to sleep beside him, Castiel fell asleep and dreamed of what he would be doing in one hundred years.
He dreamed of darkness.