Title: Free Will

Summary: Castiel strives to understand humanity just a little better in his last moments on earth. 5.22 spoilers.

A/N: Just a silly little piece that popped into my head musing on the potential motivation for one of the most elegant lines ever scripted for Supernatural.

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This was it.

If he understood anything that was happening in this confused mess of reality that he'd had to accept, for lack of contrary evidence, as life, Castiel knew that this was the moment to which everything had been building for months – years, decades, centuries, even. This moment, in this graveyard, in this tiny, insignificant Kansas city. Now. Dice had been rolled, wheels had been spun, cards had been played, game pieces had been moved and trapped and bribed and tricked into place, and it had all resulted in this instant of time and reality in which he stood.

Castiel had long since moved beyond regret at the roll he had played in this – his previous blind allegiance to Heaven, his failure to find his Heavenly Father, his inability to save so many of the brave and foolhardy humans who had fought alongside him and the Winchester brothers. His friends. He had finally grasped some small measure of just how immense this string of events was. The path to this endgame had been laid by so many hands, demonic and angelic, and for so many years that the effort to find its origin was superlatively futile.

What part God had played in all of this, Castiel no longer would even try to know.

And so, here he was, at the Apocalypse. The End of Days. It was not as Castiel had thought it would be.

He and Bobby Singer approached the three bodies and five individuals who stood amidst the dead, tied together by destiny and choice and love and hate and brotherhood. Five brothers. It was a beautiful, awful symmetry. Castiel watched them carefully, gauging the course of the interaction.

Dean Winchester. That shining beacon of humanity for whom Castiel had abandoned everything, trusting to follow in his mortal light. Dean, with his stubborn refusal to back down, a persistence so relentless and so thoughtless it could not be called bravery. He had not come here to fight the devil or end the Apocalypse or save the world, not really. He had come here because that was what he did, was what he had always done, when his brother needed him.

Sam Winchester. An abomination, Castiel had named him once. He thought he would take the words back if had the chance now. Sam was living evidence, if any had been required, of the manner in which the road to Hell was paved. But he had only ever hoped to help. Castiel could scarcely see him anymore. Sam was trapped inside his own body, barely able to struggle against the presence that held him there, the fallen angel to whom he had bent his head.

Lucifer. One of the brightest of the Heavenly Host, once, before his Fall. He had been so beautiful. In truth, he still was. He wore Sam's body with a casual and careless ease, but in Castiel's eyes, he blazed with glory and fury and light and darkness. And visible within the darkness, Castiel saw with disconcerting clarity, were scars on his very being, marks of the millennia he had spent imprisoned in the place they had hoped to return him. The scars set him apart from the brighter light of his elder brother.

Michael. He burned as brightly as any of his brethren Castiel had ever known. He outshone Lucifer as a forest fire does a candle. There was no darkness anywhere within him. And yet this light did not greet Castiel's eyes with the accordance it once had. It was powerful, yes, but also terrible and cold. There was no compassion within him, no feelings for the humans his Father had so carefully cultivated. He was a warrior of God, and nothing more. He wore his vessel with an air of distaste, a reluctance to come into contact with this base flesh.

Adam Winchester. The vessel of the archangel himself. The youngest Winchester brother, come both too late and too soon into this world of unearthly struggles into which his father had borne him. He was a dim smudge in Castiel's vision, even less capable than Sam had proved of resisting his angelic possession. Too tardy had he come to the realization that he had not truly understood the choice he had made with such confidence. Now, faced by grim reality, he was fearful and full of confusion. And… out of place.

Adam had been an afterthought. A substitute, a proxy, a replacement for Michael's true vessel. He was useable, but not ideal. And he did not – quite – belong. He was a slightly sour note in this empyrean melody that had been orchestrated for them all.

Castiel would not allow himself hope, that insidious emotion that he had learned from the Winchesters to first trust and then abandon. But he recognized opportunity. They could use this.

As Lucifer moved Sam's features into a scowl of real annoyance at Dean's presence, Castiel halted, spinning Bobby around and looting furiously through the bag of weapons he carried. They had been charged with the impossible task of creating five minutes for Dean to attempt to speak, one last time, with his brother. As if one fallen, practically human, angel and an all-but paraplegic old hunter could force an archangel and the devil to do anything they were not inclined to do. But, against all probability, Castiel had found his opening.

He would not allow himself to really think about what he was about to do. If he had, he surely would have come to his senses, holding back out of respect for his brother or from the pure overwhelming fact that there was no way in Heaven or on earth that this could be a good idea. Dean had asked for an opening, and Castiel had promised him one. This was the best chance he had yet seen at attaining that goal.

He found the bottle of holy oil he had been digging for, and snatched it up, screwing open the top as Bobby turned to him sharply, his expression clearly demanding to know what Castiel was up to. Castiel paid him no heed. He could not waste the time, and he dared not draw Michael's or Lucifer's attention too soon.

Castiel hurriedly ripped at his shirt, tearing a long strip away along the base. He carefully poured a splash of the oil down the scrap, stuffing the end of the scrap down the top of the bottle. He raised his head in time to see Bobby's eyes widen in shocked understanding of what the fallen angel was proposing to do. Castiel spared a hurried glance for the confrontation happening in front of them, seeing Michael's righteous wrath rising across Adam's face. He dove a hand into his trench coat pocket, fingers finding the lighter that Dean had given him.

Dean. One simple little human who, within months of knowing him, had ripped the ground out from under Castiel's feet and torn his self-assurance to shreds. He had been so certain, before. He had been following Heaven's orders for the greater good. How could there possibly be any wrong in that? And yet Dean had opened his eyes, shown him that sometimes the greater good simply wasn't good enough. If Heaven said that one million people had to perish to save two million, prior to meeting Dean, Castiel would have unequivocally and without hesitation wielded the sword himself. It was logical and necessary and, really, ultimately merciful. The decision, Castiel had felt, was not a difficult one.

And then he had encountered Dean, who steadfastly looked him, him, an angel of the Lord, straight in the eye and said, No.

No. I choose another way. A way that will not cost lives, though I risk my own to find it. No. I will cause the death of innocents, not in the name of Heaven, Hell, or anything in between.

Dean had forced Castiel to see what it meant to be one of the million who had to die. He had forced him to come to know these human charges of his. And then they were no longer numbers. It was not, "One million must die." It was, "Jo must die, and Ellen must die, and Bobby, and Chuck, and Amelia and Claire Novak, and even the waitresses who smile wearily at their customers as they toil away at diners all across America, innocent though they are of any real wrong, ignorant as they are of the very existence of the Apocalypse, all of them will have to die." And, Castiel found, he could no longer be so certain of the greater good.

Dean had redefined right and wrong for him. It was as simple and as immense as that. And Castiel had made his decision, had cast in his lot, and had chosen to give his allegiance to Dean, to trust in his guidance and leadership, to follow in his stride. And, even if they would not succeed, well. At least Castiel would die knowing that he had fought for what he truly believed to be right.

He held the lighter up, allowing the gravity of the moment to wash over him. There was no chance he would survive this; he was preparing to Molotov an archangel. When Michael returned, as he would in certainly no more than the five minutes Castiel had promised he would create, he would be dead. Michael was not known for his patience or his mercy. And Dean needed every second to have any chance of reaching Sam, held deep in Lucifer's grasp, at all. The next words Castiel uttered – they could be his last, as far as Dean knew.

The fallen angel closed his eyes, searching for the right words to use to call Michael's attention to him, wanting to prove to Dean that his lessons in humanity had not gone unnoticed. He needed to show Dean exactly how much everything he had done had meant to Castiel, to let him know that Castiel understood, now, everything that Dean stood for, and that he stood behind him, ready to follow him to the death, ready to give him everything within his fading power to give. Dean would hear him and understand, and it would give him one last ray of bittersweet happiness on this last day they had on earth. He would die knowing that Castiel was his.

This was the closest he had come since his fall, Castiel realized, to seeking revelation. But there was no revelation. There was only Dean.

Dean, who was taking on Lucifer and Michael both for the sake of simply saying goodbye to his brother. Dean, who had made his entrance onto the solemn scene blasting a rock song that didn't even have proper words at its beginning.

Castiel paused. The lesson was more complex than this. He had still not gotten it exactly right.

Dean… He does not follow orders blindly and subserviently. He, too, once had a father to whose will he bent, but at John's passing, he did not seek out a new leader. He took control of himself and did what he found to be right.

This, this was what was at the core of the lesson of humanity that Dean had been so long teaching to Castiel. It was not about who he followed, to whom his allegiance was pledged this week. It was about what he did for himself. It was about personal responsibility.

This was what free will meant, then. Castiel could know that it was fated that he would die here, in this sad little graveyard, but it did not mean he had to go to that fate quietly and meekly.

So, then. One last little act of defiance. In this way, Castiel thought, as he flicked the lighter on and lit the top of the cocktail, are such small victories won.

He strode forward as Michael advanced on Dean, fury in the archangel's every step. He pulled his arm back to throw.

For you, Dean, Castiel thought.

"Hey, assbutt!"

Free will. So powerful a concept. So simple an execution.

The Molotov cocktail spiraled through the air, striking Michael directly in the chest. As screams echoed from both Adam's and Michael's throats, Castiel could see, from the look of incredulous surprise in Dean's eyes that, again, he hadn't gotten it quite right. But that was oddly comforting. This was, after all, the way of things. Castiel would ever be Dean Winchester's student in the lessons of humanity, and he found he was comfortable with the situation just as it was.