A/N: It's not that I think this will happen. It's just that I wish it would. Spoilers for 14x8, ye be warned!
Thanks for beta-reading, Aini NuFire! If y'all like fix-its for this pickle Cas has gotten himself into, stay alert for one from Aini titled Never After. (I cried.)
It happens exactly the way the Empty god said it would.
By the time the chaos calms down long enough for Castiel to even think about being happy, he's almost forgotten to be on guard. It's been years.
He never forgot the deal—how could he?—but the exact moment it happens comes without warning, without mercy, without time to prepare or say goodbye. One moment he's with the Winchesters and Jack as they kick back in the Bunker, enjoying the fact that the world is safe from every recent catastrophe.
The next moment, Castiel can't breathe as his lungs fill with darkness and sludge. He's lifted from his seat as his family throws themselves backwards in shock.
"I told you," his own mouth says, but it's not his voice. "I wanted you to suffer. Now you will."
"It's the Empty," Jack gasps, as Castiel feels the alien presence stretching his mouth into a grin.
It almost feels like when Lucifer possessed him, controlled him, but worse. So much worse. It's the end of the line and they're out of miracles.
"Smart boy, you remembered me," the dark presence replies, distorting Castiel's voice into something cruel and ruthless. "Goodbye, Jack. Consider the debt paid."
Castiel would lift his chin in stubborn defiance, but he can't move his own body because he is the Empty now. He would say goodbye to his friends, apologize that they have to see this, but his voice is no longer his own. It's already taken him, and though he pretends otherwise, Castiel is afraid. And he is heartbroken. Exactly as the merciless deity wanted.
At least Jack is safe, though. The Winchesters may mourn, but they'll move on. The world will move on. Jack still has important and magnificent things to do, but Castiel is just an angel, and it's better this way. That thought is what keeps him strong.
But Dean straightens, looking grim rather than shocked, and Sam's eyes have narrowed to slits of flint.
"You can't have him," Dean says as he steps forward. No weapon in hand, no trick up his sleeve. Just his own body which has no power to stop a god.
"Oh, but I can. He offered himself to me."
"We know," Sam seethes, drawing even with Dean. "We knew you'd come. And like Dean said: you can't have him. He matters too much."
But he doesn't, and Castiel knows it. Not in the grand scheme of things. Sam isn't finished though:
"He's our family."
"Our brother," Dean adds.
Jack steps forward. "He's my father."
Castiel feels a lump in his throat, their words touching his heart even though he knows nothing is going to stop what's happening.
"Guys," Sam suddenly says. "Now!"
And then a brilliant light fills the Bunker, bright enough that even Castiel's eyes squint against it, controlled by the vicious deity. When it clears, he's stunned, but the Winchesters don't seem to be.
Duma stands with her head raised. "You can't have Castiel," she says. "He helped save Heaven. He's one of us."
The souls around her, ghosts of the humans they used to be, are a unified front.
"He protected me," Kevin informs the Empty god.
"He's an idjit, but a good one," Bobby declares.
John's smile is crooked and cool, but the shrug is light. "He guarded my boys. I owe him everything for what he's done for them."
"He's my bestie," Charlie says with a jaunty grin. She tips Castiel a wink.
"And he's good." Kelly's soft expression lights on him. "I knew he was the one to trust with my son, and there was never a more faithful angel."
His heart is in pieces, but each person to speak holds a piece in their hand and joins it back together again. Castiel's eyes fill with tears; he'd never expected this. How was this even possible? How had the Winchesters known? Not that it matters… the foreign presence isn't going to leave him just because of them. And none of this changes the fact that he doesn't matter enough to fight the deity over.
More light fills the Bunker.
"I'm not one for all this bromancing," Crowley says, eyebrow raised. "But the choir boy is the buddy to my comedy."
"He's my unicorn," Meg agrees. Her eyes twinkle, her face aglow. "Hiya, Clarence."
But the demons should be in the Empty themselves, a fact that the deity seems to be thinking as well, judging by the way it draws Castiel up in rage. The angel's arms are spread out wide, his body hovering a foot off the floor as the god emits a low rumble.
"I hate to disagree with you, old chap," Balthazar speaks from the newest streak of light that solidifies into a half dozen new forms. "But you see, he's actually ours. Castiel is my best friend, and I don't even have best friends."
"Mine as well," Anna declares. Her face is peaceful and her smile is warm. "Castiel always did what he believed to be right. Nothing that happened between us can ever change that he's my brother."
"My general who I would fight and die for," Hannah puts in.
"My idol," adds Samandriel with delight in his boyish features.
"He's the one who gave me a chance." Gadreel's stalwart face is lifted, the lines of grief and self-loathing erased. "Castiel gave me redemption."
This time the light shines even brighter, and more humans are standing in the Bunker, looking around in surprise.
"Oh," Claire says with dry acceptance of the unusual circumstances. "Is it time?" She turns to Castiel's floating form. "You must be that guy from the Empty. Well, I'm here to tell you, you can't take Castiel. He belongs here. With us. He's the one who watched over me even when I wanted to hate him. He's my guardian."
"And a fine one, I might add," Rowena purrs. "It's not every day ye find an angel who'd go out of his way to protect a witch."
"He's my friend," Mary says, tossing her head defiantly as she crosses her arms. "One of my boys."
"He saved our lives," Maggie announces with a brave lift of her head. "Me and all my friends from the other world. None of us would be here if not for Cas, and we never really even thanked him for it. He never acted like he expected us to. But he saved us anyway, because that's what he does. Because that's who he is."
Castiel feels himself gasping for air through the thickness of the emotions that fill his being. The anger of the Empty god grows with every word, but so does the warmth in Castiel's heart. He and Maggie have barely spoken a dozen words to each other; he never imagined that she would have cared about him one way or another, but there's genuine fondness in her eyes as she looks at him now, and her words are unscripted.
This time, the flash of light is filled with gold. Castiel chokes back a small sob as Gabriel's smirking face tosses him a cocky nod of reassurance.
"You can't have him," the Trickster archangel says. "Cas is a huge pain, let me tell you. But he's my little bro. And no one's taking him away, not even you. I wasn't always the best brother in the world, but you bet your ass I'm gonna stand between you and him now."
Neither of the Winchesters have even twitched at each new appearance. They've done this, somehow they've made this happen. But Castiel is starting to wonder if it's all a trick, some last act of cruelty from the deity to make him believe this was real. Any moment, he'll reveal that Castiel is already dead and none of this has happened.
But the vision doesn't dissolve, and now a cloud of black smoke swirls into the room. Castiel still can't speak with the invading parasite controlling his body, but he stares in disbelief.
Amara's eyes are as deep as the darkness that continues to swirl around her. Her voice is a gale, the roar of a hurricane. "He's my nephew."
And though Castiel knows what's coming next, he still doesn't believe it as one final voice whispers softly over Amara's storm:
"He's my son."
All else falls still.
Chuck stands beside Amara, the Winchesters stepping aside so that the two can approach. Her darkness and his light softly twist and spiral around each other in a balanced dance. She is dangerous and fierce; he is calm and steady.
The Empty god shrieks.
"I don't care! He's mine. He agreed to the terms, and he belongs to me! You have no power in my realm, old man."
"But we're not in your realm." Chuck lifts a hand. "This is mine. And so is he."
Castiel is on fire, and not even the invading god can stop the scream that rips itself from his throat. At first he thinks the deity is the one hurting him, an act of defiance towards Chuck, but then he realizes the pain is localizing on his forehead. He feels the symbol etching itself into his true celestial being, burning brightly like molten gold.
And then the pain fades and he slumps, panting. Even without being able to see, he knows that Chuck has left his mark on him.
"He's claimed," Chuck says, still soft.
"No! MY claim is the one that holds! My power is stronger than yours!"
"Perhaps. In other ways. But in this?" Chuck shakes his head. "There is nothing stronger. My love is fiercer than your power. It holds truer than your bargain. And it will outlast everything… even you. Castiel is loved. That mark is powered by their love for him, and sealed with mine. Nothing you do can break that now."
The dark, empty power that fills Castiel is writhing and screaming, terrible enough for the humans present to cover their ears in pain. His body contorts and seizes, violent spasms nearly ripping him apart. And then Castiel falls to the ground, curling in on himself as he feels control return to him.
From the floor, Castiel sees those who've come to speak for him step forward. The black, amorphous blob hanging over him shifts backward as they advance. Soon there's a line of souls and friends separating him from the deity.
"The angels come to ME when they die!" the black blob shrieks.
"And you've had them long enough," Chuck replies, sharper. "But now I've woken them up and they've fled the Empty, without you there to stop them. From now on, they'll return to me." He reaches back, clasps Amara's hand. Together, their yin-yang of smoke and light intensifies until the very air crackles. "Now go," he commands. "You don't belong here."
The deity howls and the world quakes and then everything is still.
Castiel raises his head. Everyone is gone, save for the Winchesters, Jack, and Chuck. All of them are breathing hard, seemingly unable to speak. Except for Chuck, who kneels down next to Castiel and touches his cheek.
"Jack told me about your deal," he says simply. "He offered to take your place if I would save you." The mightiness in the air falls away as Chuck rolls his eyes and snorts. "Like father, like son. Honestly, you guys, can you stop with this already? None of you are less important. I need all of you here, protecting my earth. So don't worry, I didn't accept his offer. Didn't need to."
"But…" Castiel whispers. His heart burns even more fiercely than his forehead does, where he still feels Chuck's mark claiming him. No other words emerge. He can't. Instead, he looks to Sam and Dean, who each offer him a steadfast nod.
Chuck glances over their shoulder. "Yeah, they were pretty peeved," he explains. "I had to tell them what you did. Figured they should know what was going on when I called in the cavalry. They wanted to do something sooner, but not even I can summon that deity or beat him on his own turf. We had to wait until he made his move."
Castiel still can't speak. He stares at his father and shakes his head in a question that he knows Chuck will understand. Chuck's face softens even more and he takes Castiel's hand, helping the angel to his feet. Then he enfolds his son in his arms, and Castiel clings to him like a child.
"Of course I love you that much," Chuck answers the unspoken question. "Doubt anything you want, Castiel, but never doubt how fierce my love is for you. How deeply all of them love you. How many lives you've touched. How much you matter."
Castiel closes his eyes, breathing in his father's love. No one moves. When the angel finally pulls away, his eyes are burning with tears, Chuck's face smiling at him in every facet in his crystalized vision.
"So long, boys," Chuck says simply.
Then he's gone.
Castiel's mouth falls open, shaky breath exhaling deeply as he struggles with everything that's just happened. Two hands fall on his shoulders and he turns to see Sam and Dean.
"Don't ever do that again," Dean growls, but his voice is worried instead of angry. "Cas… don't you know that we'd fight for you as much as we'd fight for Jack?"
"Did you think we'd just let it happen?" Sam presses. "Look, I get it. We've all made the sacrifice play. But sometimes you act like that's the only play you've got, and it isn't. This family isn't whole without you."
"I'm- I'm sorry." Castiel's voice is rough; he clears his throat. "I'm sorry."
They bring him into a hug, two more arms quickly joining in as Jack's presence enters the mix. Castiel considers reminding the boy that he'd promised not to tell about the deal, but then realizes that he only specified Sam and Dean. Jack seems to have learned about loopholes as well as any Winchester.
The mark on his celestial being burns brighter—not painfully, just… brighter. Warmer. Full of the love that powered it, the love of his family and friends who had come to defend him. Protect him. Fight for him, as he had fought for them.
Castiel has questions about what all of this means: whether Crowley and Meg have been returned to the Empty, where exactly the departed angels are if they returned to Chuck, whether any of the less friendly ones had also awakened and fled.
But they'll figure that out later and deal with it in due time.
For now, Castiel is still reeling. He's amazed. He's off-balance. He's claimed.
And he is fiercely loved.