The Last of the Real Ones
Jack curiously examines the angel standing in front of him. The vessel isn't the same but there's something familiar about the angel's presence—in their grace, in the shape of their wings, in the intensity of their stare that's equally examining him; there's even something familiar and all the same in completely different blue eyes. "Castiel?" he asks cautiously; optimistically.
The angel starts, a flicker of surprise flashing across their face before a neutral mask slides into place, then they—he—speaks in a low, gravelly voice: "How do you know my name?" And, yes, Jack can't help but smile at the sound because that, too, is unmistakably Castiel; not his Castiel but a Castiel and maybe some hope can be found in that.
"You're my father," Jack says simply, smile brightening even more.
"I am not your father," Castiel answers coldly and emotionless. "Lucifer is your father."
"No, he's not." Jack can't help the loss of control over his powers and knows that his eyes have grown gold in anger at the idea that Lucifer is his father when Castiel's own eyes glow blue in response as a warning. Castiel's weapon tenses in his hand and that's when Jack finally releases a breath and forces himself to calm down, reining in his powers, and then speaks again. "He is, but he's not my family. But you—the other you, I mean, from my universe—you're the one I chose."
"I don't understand what you mean," Castiel says, still seemingly indifferent, but Jack is determined to get through to him because he knows that he can and so he takes a small step toward him.
"I chose the other Castiel to be my father, to protect me, and he has. Just like he protected my mother. Just like he protects Sam and Dean. Just like he protects everyone." Something minute changes in Castiel's expression like the neutral mask is wavering ever so slightly and Jack chances another, bolder, step toward Castiel, who doesn't move forward in aggression but doesn't back away in defense either. "He isn't like any of the other angels I've met. He helps people. He cares. He's... He's good." He inches a step closer and looks beseechingly into Castiel's eyes. "I think you might be too. Maybe together we—"
A sound of rustling leaves in the distance behind him tears both of their gazes to it and when Jack looks back to him, Castiel is gone.
Castiel doesn't know why he does it, but he disobeys. He lies. He tells his superiors that he found no sign of the Nephilim in his sector. His voice is calm, his tone is even, there's no inflection nor change in his expression, no hint of emotion to give himself away.
But for the first time, in a long time...
He feels.
The next time that Jack sees the other Castiel, he's shoving his Castiel—unconscious—into his arms and bellowing, "GO!" as he guides them toward the portal. Sam, Dean, and Mary were already through it; Jack had forced them through moments before, vowing to get them home first. Now this Castiel was returning the favor and saving him— them.
There's so much that Jack wants to say to him, ask him, but all that comes out is, "Thank you."
The other Castiel nods in return, hand lingering on his shoulder as if to make sure he's okay much like his own Castiel would. Then he's shoving them through the portal. The last thing that Jack hears is the other Castiel shouting, "I'll hold them all off."
Castiel watches as Jack and the other version of him disappear through the portal before that, too, dissipates. His Lucifer, and Gabriel, and Raphael are all dead. The other universe's archangels are all gone and no threat. Michael has no means of opening the portal on this side anymore. Castiel is sure that won't stop him from trying anyway or continuing to raze their Earth to the ground, but...
Meeting Jack... Seeing the other version of himself... Knowing what they, and the Winchesters, had accomplished in their world... Knowing that the apocalypse can be stopped and that the archangels can be defeated and that this world, the people on it, even his fellow brethren don't have to be doomed... Knowing that it isn't hopeless and that everyone can be saved... That he can be saved...
That he already has been.
He finally has something to believe in again, to fight for again, to die for; more importantly, to live for.