It's like a bad romance, at least that's what Dean would call it.

Firstly Lucifer is his brother; sure a brother he has never seen before he fell from Heaven and Lucifer rose from Hell but the point still stands: Lucifer is his brother.

Secondly beyond both of them being fallen angels they have nothing in common. Lucifer doesn't see the worth Castiel has discovered in humans. They never agree on anything and despite his contempt for them Lucifer knows more about humans and their culture than Castiel and if it weren't for the Apocalypse Castiel often catches himself thinking that Lucifer and Dean would get along splendidly.

Thirdly they're enemies. There is no way around that either; Lucifer wants to destroy the world, wants to annihilate humanity and Castiel has sworn to prevent that. He actively works with Sam and Dean on a way to kill Lucifer or at least to stop him permanently. Yet, whenever Lucifer calls to him Castiel follows; follows to obscure corners of the world far away from Sam and Dean, far away from any human being.

The presence of another angel is different than the presence of a human. Castiel appreciates Dean's and Sam's friendship but they are not and never will be angels. An angel's grace is a piece of Heaven, a part of Paradise and when they meet Lucifer and Castiel find comfort in basking in each other's grace remains.

/

This time it's different. Castiel knows as soon as he steps into the small church on Aruba. It's the 2nd February, Candle mass and the whole church is lit with hundreds, maybe a thousand candles. Lucifer kneels in front of the altar and in the soft, warm firelight which hides his wounds, Castiel can see the most beautiful angel his father ever created shining through the vessel that is slowly falling apart from the inside.

"They have never seen him," Lucifer says softly: "And yet they still believe." He rises to his feet and turns around to Castiel: "Just like you."

"Is there a point why you have called me here?" Castiel asks impatiently.

"Of course there is." Lucifer answers calmly.

Castiel tilts his head, waiting for him to continue.

"This is the last time we will see each other like this. You're becoming more human every day and the smell sickens me."

"I understand." Castiel says almost dismissively which makes Lucifer look at him curiously:

"You don't mind?"

"I mind, I just don't care."

"What a curious thing you are."

"You said that before." Lucifer shrugs and crosses the distance between them. The smell of Hell is still strong around him, stronger than it is on Dean but that is to be expected.

"I thought for tonight we could..." Lucifer stands very close and raises a hand to lie against Castiel's cheek. It's a strange gesture because they've never touched before and Lucifer looks unusually vulnerable and scared when he does. Castiel knows what he wants; he spent enough time around Dean.

"We are not humans." He reminds Lucifer.

"No," Lucifer amends: "Not yet in your case."

"We are brothers."

"Are we?" Lucifer leans his forehead against Castiel's and whispers: "You are the most beautiful angel I've ever seen, a rare, exceptional gem. I would not have left Heaven without you had you been born before my Punishment."

These words, these compliments are new for Castiel. He has never been exposed to such praise before. Tilting his head to touch his lips to Lucifer's is only a tiny movement but it feels like a momentous occasion.

It feels like the end of the world.

And in the middle of a thousand and one candles burning for their absent father sin is heaped on sin. They don't speak another word and they don't need to. They both know that this is the only time, that they may never be able to even look at each other after this.

They also know that they would be a wasteland without it.