"Dean?"

Castiel was walking into the dark vault carefully, with slow steps.

Suddenly, two arms caught him from behind, with a strength even him couldn't fight with. The shock made him drop the angel blade he was holding.

"Well, well, Cas, I didn't think you were so idiot as to come here looking for me all by yourself…"

Castiel felt his heart skip a beat when he heard Dean's voice. He always had been able to recognize him, he always felt his presence the same moment he showed up. But not this time.

This time, he felt nothing. And that frightened him.

Dean seemed to notice his discomfort and fear and let out a sarcastic laugh.

"Oh, c'mon! You didn't come this far –obviously with the idea of a quick fuck since you're apparently so obsessed with me, just to let yourself be scared so easily. I remembered you more brave Cas, don't disappoint me!"

The angel closed his eyes when he heard Dean's words. He knew it was the demon talking, but even so it was so disturbing to hear how natural it seemed to sound from Dean. It was as if he had been a demon all his life…

"I've come to help you, Dean" he got to articulate, trying to make his voice sound as neutral as ever.

"Helping me? Really? You?" mocked Dean, and then Cas felt the First Blade touching his neck, but without actually hurting him. That's what he was expecting. "You couldn't help me, Castiel, even if you were the last angel on Earth. Which, by the way, is very likely..."

"I can help you, Dean, and I will" stated Cas.

And with that, Castiel dropped his head forward, making the First Blade cut a deep wound on his neck, just in the same place Metatron had cut him to steal his Grace. From the wound started to sneak out the few Grace that remained on Cas body, staying suspended in the air.

Dean moved away from Cas in that moment, the image of an angel's Grace too stunning to being seen for the first time through a demon's eyes.

Cas took that moment of freedom and confusion to quickly remove the First Blade from Dean's hands and, before the demon could react, he passed it through the Grace, making the Blade absorb it completely.

A growl from Dean made him turn around.

"What the fuck you just did?" asked Dean, slowly, giving threatening steps towards him.

Cas found hard to speak and to stay standing. He had just given up the last Grace he had left, and he didn't know how long he could handle it. But the mission wasn't over. He couldn't rest. Not yet.

"Dean, if you let me, I can…"

"Give me the Blade" said Dean, not giving Cas time to speak. Being without the Blade hurt him. He needed it.

"Dean, please…"

"GIVE IT TO ME!"

Dean moved his hand as he shouted and Cas was thrown to the opposite wall of the vault, crashing hard against it. Dean approached his body, now lying on the floor. He was going to take the Blade back and maybe even end once and for all with that poor lonely angel…

But then Castiel opened his eyes, and in just one quickly move, he scratched the Mark on Dean's arm with the First Blade.

The scream of pain that Dean made was breathtaking.

The Mark of Cain burned inside of Dean, like if it wanted to consume him inside out. The Grace that had been inside the Blade was transferred to the Mark, and were now fighting inside of him, trying to gain control.

Finally, a light came out of Dean's arm, forcing him to close his eyes again and making him feel like he was being pushed by an invisible force.

When he could open his eyes again, he looked at his arm. It was bloody and hurt him, but that didn't matter. Because the Mark of Cain was gone.

Dean felt like his head was finally being freed from all the clouds that didn't let him think straight since he got the Mark. He was free from the desires to kill, destroy, and hurt. He was himself again.

A weak moan made him come to reality again.

"Cas!"

Dean run to where the angel was still lying on the ground and knelt besides him.

"Cas, no… No, no no" mumbled Dea. He understood what just happened. He knew that Cas had given up his Grace in exchange of his freedom. And he knew what was going to happen to him now.

He knew it, but he sure as hell wasn't going to accept it.

"Hey, hold on, okay? I will get you help. I will call Sammy, I'm sure he knows how-"

"No, Dean" said weakly Cas, holding Dean before he could go looking for his phone. "It's not necessary, it wouldn't work. I know what must happen to me, and it is okay."

"No! No, it's not fucking okay. You will die, Cas! Without your Grace you will die, how the hell is that okay?!" shouted Dean, trying to keep his tears from falling from his eyes.

"Because I have for once done something good, Dean. I've saved you. That's good, that's okay…" said Cas with a little smile, being able to watch again Dean's green eyes.

Dean ducked his head, feeling the tears finally falling.

"I don't want you to go, Cas…" he whispered, touching Cas face carefully.

"I know. And that's more than I would have ever dreamed for, Dean Winchester…"

And Castiel, the Angel of the Lord, closed his eyes forever, the human for whom he had given everything he had, being the last thing he would ever see.