Mercy
"No... no, Cas, please..."
"Dammit, Cas, don't do this!"
"I warned you what would happen if you persisted. Goodbye, Sam."
Sam lay prone in the darkness, chest heaving as he gulped in deeper and deeper breaths. He refused to move, limbs twitching involuntarily as he stared at the nothingness beyond him. After everything that happened... Sam had believed in him, trusted that he would never even attempt something like this. But he had changed, something had changed him and whatever had made them friends before was gone for good. And so, it seemed, was Sam.
The heavy plunk of shoes approached his left, and Sam twisted his head a fraction and gazed dully upwards. There was Lucifer, towering over him and glancing down with an ecstatic grin. Sam gulped and closed his eyes, waiting for the torture soon to follow. He wouldn't cry, not yet. He had an eternity left, after all.
He was back.
Cas sent him back.
Author's notes: I know this is completely OOC for Cas, even God!Cas. But the idea would not let go.