Sam studies the First Blade. If he hadn't seen it used already, he'd have some doubts about this supposedly ancient jawbone. It looks like it should be crumbling in his fingers.

Weird to think he's about to have this in common with the first ever younger brother.

"Dean." Sam turns around to face Dean and holds out the Blade.

Dean has learned to (mostly) control the power of the blade; it's safe for him to handle it now. He reaches out a few inches with a trembling hand, then takes it back, shaking his head.

Sam takes a step closer.

"You have to do this, Dean. The blade won't kill Abaddon if you don't kill me. And we agreed," he says. "This is it. This is what we mean when we say we'd do anything for each other. I'm begging you here, let me help kill Abaddon."

Dean blinks back tears as he accepts the Blade.

"I know. I- I will. Just… give me a minute." He bows his head. It's a damned long minute. The only movement is one tear falling.

Finally he looks Sam in the eye again. His voice is broken as he asks, "Are you ready?"

"Yes." Sam adjusts his stance, braces himself. He's fine with the dying part. What he's not ready for is seeing the pain in his brother's face as he plunges the First Blade into Sam's heart. Worst of all, the knowledge that he has to go to Heaven without Dean. That part, he'll never be ready for. Nothing can ever make that right. The more he thinks about it, the weaker his resolve to go through with it becomes.

Dean looks Sam over like he's deciding whether to tell Sam to turn around. Sam is about to ask when Dean drops the blade.

"Sammy, I can't kill you." Tears stream down Dean's face. "I can't do it when I know you're not coming back."

Sam takes his brother's face in his hands and presses his lips to Dean's forehead briefly. He lets go and picks up the blade.

"You can do it, Dean.

"Do it for me."

Dean grips the handle of the Blade.

"Do it for Dad. Do it for Mom."

Sam closes his hand around Dean's as the Mark of Cain begins to glow.

"Do it for the Vine."