"I can't," Castiel growled. "He's shown me. The power he can weild, the way he can fight it... Lucifer is the only chance we've got."

For a second, his hands were his own, and he stroked Dean's cheeks, urging him upward very slightly, his eyes so full of his own pain and fear, but absolute certainty.

"I won't deny I've made mistakes before. I have. But this is different, Dean. Even if he burns me out, even if there's nothing left, it would be worth it. Endure this, don't let him win. Do you understand? Please--"

Castiel's expression fell away, and Lucifer pushed Dean back. "I think that's enough soul bonding, hm? I've had enough of his mouth--and yours."