God was dying, the sun was wasting away, Dean was preparing to sacrifice himself, and Castiel was standing in a cemetery, watching the events unfold. He had tried so hard to be useful. He had given his vessel over to Lucifer, endured seemingly endless torture at the hands of Amara, poured his grace, his very being, into stopping the Darkness. But it had not been enough.
Tears started forming in his eyes as Dean and Sam embraced for the last time. Tears were such a human thing, but that was what he had become. No, he had become less than human. People were able to try, to make something of their short lives, to be someone. Castiel was no one. He was a name attached to and empty shell. He had once had eyes filled with wonder and hope, looking out over his Father's creations. But his Father was dying, the world along with him.
Dean came over to him, preparing for his goodbye. Castiel wished he could fly away, he didn't want to look into the eyes of the man he had failed to save, but his wings were useless and broken, like the rest of him.
"Dean, I'm.. I.."
"Don't say it Cas. Don't say goodbye. Don't say you're sorry. I wouldn't have had it any other way."
And suddenly Dean was kissing him. The Hunter's rough lips were mashed onto his own and Dean's tongue was seeking entry into his mouth. The Angel let him in, and held him close. This may have been their first and last kiss, but the years since that fateful day in the sigil covered barn were echoing between them. The sun may be dying but it didn't matter, because a thousand galaxies burned bright where Dean was touching him. After what seemed like forever, Dean pulled back. He opened his mouth, then closed it. No words were spoken. No words were needed. As Dean walked away, Castiel smiled. Here, at the end of all things, he had finally realised why he felt so empty. He was only a half of a whole, one side of a bond, and he vowed that he and Dean would never be separated again. He knew that no matter what, no matter who won or who lost, Dean would be there. Heaven and Hell could perish and fall, but his Hunter would always find his way back to the Angel.
Castiel walked over to where Dean was standing and placed his palm over the mark on his shoulder. Energy poured out of the human and wrapped around the Angel's back. Placing his hand in Dean's, Castiel nodded. The two looked towards their family, and their family smiled back. Tears would be shed and the grievances would be long and hard to suffer through, but for a moment the world stood still. Then Castiel spread out his newly healed wings, gripped Dean's hand tight and flew.