Eventually his body began to still, the tremors subsiding, and he paused, sniffling, before drawing back to look at me. "I'm sorry, Sir. I don't know what came over me - I…"
I waved a hand to cut him off, shaking my head. "There's nothing to apologize for, Cas. I think it's pretty understandable, after everything you've been through."
He sniffed again, rubbing at his watery eyes in an almost childlike manner. "Regardless, I should not have acted that way."
I reached out gently, touching his hand with my fingertips, flinching when he startled. "You're safe with me. You don't have to pretend."
He looked away, taking a deep, sobering breath. "I… I hate this. I hate it. I'm not strong enough," he admitted in a low whisper, gaze brimming once more as my heart trembled.
"Are you kidding? You sacrificed yourself for thousands of people. You're the strongest person I know," I replied, my own voice a reverent hush. He smiled weakly, finally meeting my eyes.
"I acted out of pride, Dean. And now I am being punished for it."
I recoiled again, pulling him back into my side. "Cas… You acted out of love. I'm so amazed by you. I only wish I could have made the same sacrifice," I added quietly, burying my face in his hair, deeply breathing the scent of this stunning, damaged creature. When he hummed questioningly, I let out a deep sigh. "I lasted as long as I could on the rack, Cas. They came to me, every single day, and offered to take me off, if I tortured those that were put in my place. And for almost six years, I said no. Every single day."
"But then I couldn't any more," I confessed, closing my eyes against the memory. "I just… Couldn't. I'd have done anything to get off that rack. And, as it turns out, I soon would." Another sigh, and I balled my hands into fists against the angel's back. "I've done… Awful things. Things that most people could never imagine - though, as a fellow plaything of Crowley, you probably could. All to save my own skin."
Castiel looked up at me, lashes spiked with tears. "Nobody could blame you for that, Dean. I imagine most mortals would take up that offer far sooner."
I nodded slowly, thoughtfully. "That's probably true. But I can't forgive myself for taking it at all, no matter how long I held out." I thought of the creature formally known as my brother, currently reclining in the next room without a care in the world. "Sam broke a little while before I did. It took no time at all for him to begin to relish the torture. He… I don't know what happened. He was just a kid when we got here - how did he end up so… Evil?"
Cas hummed, his cheek resting against my chest. "Samuel Winchester… That's a soul with an interesting history."
I pulled back sharply, fixing my eyes on his celestial ones. "What do you mean?"
Castiel frowned, eyebrows knitting together. "You don't know?"
"Know what?" I countered, baffled. "And how do you know anything about him?"
He shrugged, toying with a fraying edge of his shirt uncertainly. "I'm an angel. We all know who he is - who you both are. Heaven had big plans for you," he added, noticing my confusion. "You were to be the vessel of the Archangel Michael, if only you'd lived. And Sam…"
"Sam?" I prompted when he trailed off, and he grimaced.
"Sam was to be the vessel of Lucifer," he admitted eventually. "A role he had been primed for his entire life. Your mother's death… Azazael… None of it was coincidence. He was being prepared for the apocalypse, to be the body of Sin."
"Azazael? The demon?" I clarified, still puzzled, but a sinking feeling settling in my chest nervously. I'd met the yellow-eyed bottom-feeder a few times, but only in passing, though I was aware that Sam worked quite closely with him.
Castiel nodded slowly, as if considering how much to share with me, before he sighed, leading me to sit on the bed. "He… The fire that killed your mother was his handwork. She interrupted him. There is an ancient and rare procedure, established for exactly the purpose of preparing a vessel for Lucifer. The infant is… Nourished with demon blood, from an early age. If Sam had survived, it's likely he would have craved further sustenance of this nature, and developed abilities similar to that of his full-blooded siblings."
My mouth worked wordlessly, and the angel offered me a sad smile. "That's why he has adapted to this world so easily. It is - literally speaking - in his blood."

I sat in stunned silence for an unknown amount of time, until I heard the front door slam without warning, shaking me out of my stupor. Castiel had bolted to his feet, trembling nervously, and I reached out to touch his hand comfortingly.
"It's ok," I muttered, my voice still thick with disbelief. "It's just Sam. He heads out most evenings - though I've no idea where," I admitted, frowning. Is he meeting Azazel? The scumbag who killed our mother?
Castiel's steady azure gaze mirrored my thoughts, and I winced. "Is it terrible that I'm glad to know this? I though… I dreaded… That my brother was just… Evil. But this… This isn't his fault, you know? He can't help his nature."
Cas hummed thoughtfully, tilting a hand. "True… And not. He can't help what has happened to him, no more than you can help being Michael's vessel. But he could refuse the calling, much as you could have, had the time come. He accepted his fate without complaint, and that was his choice. If you don't mind my saying so," he added, mouth tightening in a wince.
I ground my teeth, resisting the urge to flash my black eyes. "If a dog is beaten, do you blame it for being aggressive, or do you blame the owner for causing the aggression?"
Castiel tipped his head curiously. "If a child is beaten, do you blame him for beating his wife, or do you blame the parents?" He shook his head, slowly, sadly. "The child may have inclinations, but his actions are his own. Cause does not negate responsibility - humans are, after all, more than simple beasts. We can choose to break the cycle, or perpetuate it."
I fought the rage rising in my chest - because after all, wouldn't that just prove him right? - and let out a deep exhale. "I… That's an interesting point," I admitted reluctantly, still resisting every instinct that wanted to vehemently protest. After all, had I not turned away from the authoritarian nature of my father, as proven by my reluctance to issue orders to the angel before me? Had I not rejected the part of my soul that longed order and discipline, in favour of health and free will for the skittish creature I found at my mercy? Following in the steps of John would have been simple and natural, resigning myself to a predetermined fate, taking the role of leader over follower, like a child taking the role of parent as they grow?
"… You're right," I admitted again, my voice quiet and without the rage I'd felt only moments before, resigned to the new reality I found myself in. "I… It would have been easy for me to accept this - all of it; to accept my role in Hell, and my role as your… Owner," I finished uneasily, an ashamed flush creeping up my cheeks. "But I refused - not because it was the easy thing to do, but because it was the hard thing. Because it was the right thing."
Cas nodded once, looking surprised and pleased. "Precisely. Inclination and nature is beyond our control, but actions… Actions are all ours."
I sighed, running a hand through my hair. "So… How do I help him? How do I convince him to betray who he is, and fallow the soul I know he has?"
Castiel smiled sadly, shrugging a shoulder. "If I knew how to turn men from sin, my job would be significantly easier."