A/N: Just as a warning, there are references to S13 spoilers in this fic.

Love's a Fragile Little Flame (It Could Burn Out)

He and Sam are in the grocery store when he hears his name screaming through his head—CASTIEL!—before it abruptly cuts off, and then a terrible, yawning absence fills him. A second later the full chorus of the Heavenly Host is crashing into his head, four words repeating over and over again; the noise so loud and intense that it blurs his vision and sends him to his knees.

A small crowd starts to gather around him; people quietly murmuring among themselves. A few call out to ask him if he's all right, but the only thing he can do is continue to clutch his head in pain. By the time Sam's familiar presence makes its way to him, the voices of the Host have receded, though the pain still remains. He hears the placating tone of Sam's voice to the crowd, reassuring them that everything's fine; feels gravity shift as Sam hefts him up and leads him out of the store.

It's only when they're outside and Sam has put him into the passenger's seat and then climbed into the driver's side himself that Sam asks him what's happened. "The bunker," is all Castiel manages to grind out in reply.

The concern written on Sam's face for him changes into something more serious and Sam becomes more alert and focused. "Is it Dean?" Sam asks, already starting the car and peeling out of the parking lot. Castiel shakes his head and then grimaces at the still-lingering pain. He grits his teeth. "Just— The bunker. We have to get back."

Sam looks like he wants to ask him more, wants to ask him about Dean, or Mary, but something must show on his own face because instead of asking anything Sam only drives faster.

Neither of them says anything during the tense ride back. Sam doesn't ask any more questions. Castiel doesn't tell him about what he heard. What he can't bring himself to say out loud. What he doesn't want to admit to himself. The fear that haunts him.

Jack is dead.

It's only after he's pulled away from Sam and Dean's hugs that Castiel truly takes in the presence of a young man in a tan colored jacket standing behind them. Brown hair falls in his face. Blue eyes study him intently. Despite never having seen him before, Castiel knows who he is all the same:

"Jack."

Jack smiles shyly at the sound of Castiel speaking his name, but it lights up his whole face and Castiel feels something in his chest tighten at the sight. "Hello, Castiel."

Castiel smiles back. "It's nice to finally meet you."

Dean is sitting at the war room table when they get back to the bunker; a cold, hard look of determination on his face. His arms are spread out on the table, hands bloody; an equally bloody angel blade rests on the table between them. Not just any angel blade either, but Claire's. A Grigori's sword. A regular angel blade wouldn't be enough to kill an archangel's Nephilim, but a Grigori's sword... It could work.

(Castiel thinks of what he's been trying to deny the whole drive there. What Jack's voice calling for him in his head must have meant. What the Host of Heaven felt just as surely as he did. The four words that echoed over and over again: "The Nephilim Is Dead." It did more than could work, it did work.)

"No." The word slips out of him, broken and cracked. Sam must realize what it all means, too, because Castiel sees his face fall.

"What did you do?" Castiel asks angrily, quickly making his way down the stairs. "What I had to," Dean says with no emotion in his voice. His expression doesn't change at all either; the same cold, hard, uncaring look never wavering.

"Where is he?"

Dean doesn't answer his question, he doesn't even get up, so Castiel moves past him and heads to the last place he'd seen Jack: Jack's room.

Jack is laid out on his bed when he gets there. The book Jack had been reading earlier open on his nightstand like he'd just put it down. His eyes are closed. There's a visible bloody hole, clearly made by a Grigori's sword, where his heart is.

"No." The word slips from him again, over and over, sounding more wrecked each time. He takes a few steps forward before collapsing next to the bed. He grabs Jack's hand and takes a shuddering breath. His hand is still warm. He could almost, almost be sleeping. But he isn't. Castiel can't hear him breathing. He can't hear Jack's heart beating, nor the blood pumping through his veins. There are no signs of life. He's dead.

He hears Sam and Dean's footsteps reach the room. Sam opens his mouth to speak but then abruptly closes it. Dean says nothing at all. "Leave," is all Castiel manages to say himself, barely holding it together.

Neither Winchester moves, though, so Castiel turns toward them, grace lighting his eyes an unearthly blue. The lights in the hallway spark and shatter. "Leave," Castiel says, true voice blending with his vessel's. He holds his free hand out and forces Sam and Dean from the room with his grace, then closes the door with a resounding bang. There's pounding on the door and voices, but he ignores it as he turns back to Jack.

He puts all of his grace into healing Jack, trying to bring him back. Blood drips down from his nose at the overexertion—mixing with tears he hadn't even noticed he'd shed—but that doesn't deter him at all. If anything, it only spurs him on and he pours even more of his grace into Jack's body as if that could somehow bring him back. Then: snip. A quiet, tiny feeling inside of him like the floor's suddenly dropped out from under his feet as his grace goes far beyond its breaking point.

He passes out.

Castiel watches Jack sleep during longs nights in the bunker when he's the only one still awake. Sometimes he'll only stand in the doorway of Jack's room for just a second; other times he'll slip further into the room and stand next to Jack's bed, then on an impulse brush a strand of Jack's hair out of his face before leaving.

But even when he doesn't physically watch over Jack while he sleeps, he still finds himself watching over Jack by listening to him. He'll sit at the kitchen table, or in his own bedroom, or in the library, and close his eyes, concentrating. He filters all the other noises of the bunker out, the sounds of Sam and Dean sleeping, until the only thing he can hear is Jack.

There's something comforting about the slow, steady reassurances of Jack's breaths. The beat of his heart. Just knowing he's... there. That he's safe.

When he comes to, the door to Jack's room is open and he's on the ground, propped up against the side of Jack's bed. Sam is slowly cleaning the blood—and tears—from his face with a slightly damp washcloth.

Castiel doesn't turn to look at Jack; he can't bear to see him that way (dead) again just yet, but he does reach back blindly, feeling for Jack's hand and then holding it when he finds it. His grace is still too fragile to attempt any kind of healing yet though.

Sam says nothing to him. He doesn't ask why there's blood on his face in the first place or why he passed out. He doesn't even look him in the eye. "Did you know? What Dean was going to do?" The thought occurs to him so suddenly that he's asking it before he's even really aware that he'd thought of it in the first place.

Sam freezes, hand pausing in wiping away the dried blood. "No." But, Castiel thinks. Sam continues: "But we did discuss it. What we might have to do if things came down to it." A cold, tired feeling of disappointment washes over him.

"But I swear, Cas, that's all it was. Just talk. In case something ever did go wrong. What Dean did... It wasn't right."

Sam moves to wipe away the blood again, but Castiel catches his hand to stop him before he can. "I'd like to be alone," he says firmly. He lets go of Sam's hand.

Sam lets out a little breath like he wants to protest in some way, but then he nods and stands up. He's at the threshold of the door when he pauses and says: "I know it might not seem like it right now, Cas, but we're here for you."

He leaves. Castiel watches him go, feeling nothing; Sam's words completely meaningless to him. He just doesn't care anymore.

He closes the door after Sam with a small amount of grace that's regenerated. He leans his head back against the side of the bed and traces random Enochian letters and words on Jack's hand with his thumb.

He waits for more of his grace to come back to keep Jack's body from rotting.

Castiel teaches Jack about his powers and his grace. He teaches Jack simple Enochian sigils and warding and spells, then more difficult ones when Jack easily masters the first. Jack takes it all in with rapt attention, a quiet but intense and eager curiosity about him; there's always something more he wants to understand, something else he wants to know.

Every time Jack looks to him for his knowledge and guidance, or with a small smile for affirmation when he's done something right, Castiel feels a swell of pride.

"I did what I had to do, Cas."

Dean stands in the doorway to Jack's room, arms crossed, wearing the same resolved look on his face that he did when his hands were still stained with Jack's blood. Castiel turns away from him and back to Jack, hand still clutching Jack's own, a slow but steady thread of his grace healing Jack's body and preventing it from decaying.

"He was evil. Sooner or later, he would've shown his stripes."

Castiel doesn't answer.

"As much as you, and Kelly, and everyone else wanted to believe… He was Lucifer's son."

Castiel still doesn't answer and Dean eventually gives up on waiting for one with an annoyed sigh. Castiel waits until Dean's retreating footsteps fall far enough away that he knows Dean won't be able to hear him, then he bows his head and clutches Jack's hand harder.

"You're wrong. He was my son."

They're sitting on a park bench, quietly watching the world go by when Jack asks him:

"Do you ever wish...?" Jack trails off as a child wails in the distance, crying out with some new hurt. "Do you ever wish that we could've had this?"

Castiel watches as the child's parent rushes over and soothes them with soft words and promises of kisses to make it feel better. "I think about it, sometimes," Castiel answers truthfully, and he does. Sometimes he imagines what it would be like to hold Jack in his arms as a baby and to watch him grow up instead of what happened: dying and only meeting Jack months later as an adult.

Castiel looks at Jack and waits for Jack to look back at him before he speaks. "But it only makes me cherish the time we have now even more."

Jack nods at him, lifting his hand and subtly sending out a small wave of his grace to take away some of the child's pain.

"I feel that way too."

Castiel thinks about what he had told Dean… so long ago now: The Dean Winchester I know would never have murdered that kid.

It's been four days since Jack died. No, not died. It's been four days since Jack was murdered, and Castiel hasn't moved from the same spot at all. He's still knelt over Jack, clutching his hand, preserving his body and keeping it pristine with a small amount of his grace.

He thinks he never really knew Dean at all. Or any of them. Or maybe he just never wanted to admit it to himself.

Until now.

When it's too late for it to matter anymore.

One of the hunters takes a single look at him and Jack, clearly sensing something Other about them and raises his gun. Castiel knows that the bullets used on Lucifer weren't enough to kill him, but that was also Lucifer. An archangel. For as powerful as Jack is, he's still not that. If there's even a chance that the bullets could hurt Jack... If there's a chance that they could kill him...

It's not a chance he's willing to take.

Castiel tackles Jack, shielding Jack's body with his own, and feels a bullet rip into him—painful, but not fatal—before they slam into the ground. He groans in pain, clutching his shoulder, as Jack moves out from under him and turns him over.

Jack crouches over him and he sees Jack see the blood and grace seeping from his wound. Jack's eyes widen at the sight and then glow gold; he snarls, head whipping toward the hunters, clearly intent on attacking. The hunters recognize the obvious threat to themselves and raise their guns just like the first had. But then Castiel's yelling and Mary and the Winchesters are raising their guns as well and everything descends into further chaos.

Finally, the alternate Bobby fires a warning shot into the air and calmly but forcefully says: "Hey, ya idjits. I said stop. Weapons down. That means all of you." The last part he says pointedly to his hunters. Everyone complies; though, Bobby's side much more begrudgingly.

Jack turns back to him once all the weapons are down and the threat has passed, worry written all over his face. Jack's hands press against his wound, but there's no pain. Instead, the only thing he feels is the familiar warm, golden glow of Jack's grace healing him. The instant he sits up, fully healed, Jack's arms wrap around him.

It's the first time Jack's hugged him.

Castiel returns it immediately, running his fingers absentmindedly through Jack's hair, stroking his head, whispering comforting words to him in Enochian.

"You sure you don't want us to come with you?"

He and Sam are standing at the base of the stairs leading out of the bunker. Castiel shakes his head. "No, I want— I need to do this alone." He's going back to the house that he had rented with Kelly. The one that he thought was going to raise Jack in, back when they thought Jack was going to be born a baby. The house that Jack had been born in. The same house where Kelly's grave now lies, and where his grave had been, to bury Jack.

Jack deserves to be with his mother, at least in death, if only that.

Sam nods, hugs him briefly, but Castiel can't bring himself to return it. "We'll see you soon, okay?" Sam says, pulling away.

"Of course," Castiel says, trying to make the words sound convincing but they fall flat and lifeless on his own ears. Because what he doesn't say is that the few belongings he has have been packed away along with Jack's body, and Jack's books and his clothes and all of Jack's things, in his truck. That his cell phone and his fake government badges and anything tying him to hunters, to this place, to them is still in a drawer in his room here. That even his trench coat—which Sam had clearly noticed he wasn't wearing but didn't remark on at all—is folded up neatly on his bed.

Castiel walks up the stairs, pauses at the door, and takes one last look around. Dean is nowhere to be found, making his steadfast position on killing Jack clear. Sam is still at the base of the stairs. Mary is standing just slightly further back from Sam. She nods to him as he turns back around to leave, some kind of look of understanding on her face that makes him think that she knows: He isn't coming back.

For how could he stay with the same person who murdered his child? The same people who would have gone along with it… eventually?

Castiel stands in the doorway to Jack's room, rapping lightly at the frame until Jack looks up from the book he's reading. "Sam and I are going to the store," he says. "Is there anything you want?"

Jack shakes his head and turns back to his book. "No, I'm fine, dad."

Dad. The word is said so casually and somehow it means everything to him. Maybe it's even more meaningful because it's said without a thought.

"All right," Castiel says. "We'll be back soon." He leaves, smiling at the mundane happiness of it all.

Castiel stares at the freshly dug-then filled grave and the hastily put together grave marker. The finality, the reality of it all—that Jack is dead, that he really is dead—hits him.

His grace crackles just beneath the surface of his skin; storm clouds gather in the night sky, lightning flashes overhead, and thunder booms. Rain starts to pour as he screams with his true voice, unleashing all of the emotion he's kept carefully restrained for the past five days.

Energy spent, he almost collapses to his knees, but at the last second Castiel steadies himself. The rain starts to turn to a drizzle. He wipes away his tears with the back of his hand and then looks to the sky.

"Father," he says, "I know I don't deserve this, after all the damage I've done, even when I've tried to make things right... But Jack... I saw the world that he could've created. All the people he could've helped. The good he could've done. He wasn't evil. He didn't deserve to die. He didn't deserve to be killed. He was good. I believed in him."

Castiel takes a shuddering breath. "But more than that... I loved him. He was my family. He was my... child." Then he pauses with an afterthought, a twinge of a smile on his lips. "In a way, he was your grandson, too."

Castiel softly runs his fingers over the grave marker. "Please, Father, bring him back."

Nothing happens.

But, suddenly, Castiel has faith. He feels it so surely, just as he did when he felt Jack's power coursing through him that first time, saving him and Kelly. He feels it just as he did when Jack showed him their future. Like he did the first time Jack smiled at him, and said his name, and hugged him, and called him not even father but dad.

Castiel knows that if just stays here, that Jack will return to him.

"CASTIEL!" Jack screams his name in his head and then there's…

Nothing.

Castiel feels the absence of Jack like he's died himself.

Castiel waits. He stands next to Jack's grave with the sun rising and he waits. He waits as he watches the sun set and then rise again and then set again.

On the morning of the third sunrise, the ground trembles for a moment and then Jack's hand is shooting out of it, clawing for life. Castiel grabs it and pulls Jack up, out of the earth, and into his arms.