Summary: Sam will do anything to save Dean. AU Season 6, episode 22 'The Man Who Knew Too Much.
Warnings: Rape, violence, dark, major character death, Godstiel is fucking crazy. Unrequited sastiel. WINCEST.
The angel blade Sam sinks into Castiel's flesh doesn't kill him. He pulls it out easily, lays it down on the table.
"I saved you from the Cage, Sam. Because I wanted to. I wanted you. And this is how you thank me?" Castiel, the New God, speaks with a chilling calm.
Dean gasps on the ground, blood bubbles from his mouth, drips down his chin. He chokes. Breathing slows. Save him.
"Please, Cas. P-please. I'll, I'll do anything, o-okay? I'm so sorry. Just. Just heal my brother and let him go," Sam begs, unable to take his eyes away from the nightmare in front of him. He's not allowed to touch him. He watches on his knees as Dean struggles for every breath.
"Say you'll be mine."
Sam flinches. Hesitates. No, not yours. Never yours. Always Dean's. "Yes," he manages. "I'm, I'm yours. Please, oh god, save him."
Hands dig into his hair, yanks his head back. He looks up at Cas with wide, tear-filled eyes. "I require proof. Make love with me first."
He chances a glance at his brother. Barely breathing. His stomach turns sickly. Save him.
Sam nods. He doesn't want to, but he must. For Dean.
But when Castiel finishes inside him, when he crawls over to his brother, come leaking out of his sore ass, Dean's not moving. Dean's not breathing.
"Can't let him live, Sam. You're mine. No one else's." A flutter of wings. Castiel disappears.
Sam curls in against his brother and finally lets the tears fall.