God, I keep thinking about a supernatural/Host AU (The Smeyer's book, it's a cool concept,- no wait, comeback! Hear me out its Destiel and also Midam)
Briefest of summaries if you don't know The Host, basically an alien race of pacifist body snatchers "Souls" takes over the planet, and like, fix all the problems in the world, from crime to starvation to polution, its just, you know, they literally had to kill all the human to do it, they just don't see it as killing because even though the mind is gone, the bodies are still alive. Greater-good sort of thing.
Briefest of summaries if you haven't watches Supernatural: a couple of brothers hunt monster all across the continental US, as well as Heaven and Hell as they they constantly try to avert the lastest apocalypse they accidently helped start, while trying to stop the previous one.
So, Cas is a Soul in the body of Jimmy Novak, and he's on the run with Claire and Jack, the 7 and 3 year old children of his host body, because last minute he pannicked and couldn't turn them in to become hosts for other souls.
He tells himself it's because saving his children was the sole motivation of Jimmy that he feels so strongly, but Jimmy's gone, and Claire had looked so scared when she looked at him and knew he wasn't her dad, and when Jack had looked at him and called him dad and had no idea is dad was gone.
He's fairly certain there are other humans out in the world, hiding somewhere and he's determined to get the kids to them, where they will definitely be safer than living around souls, who, while wouldn't hurt them, do keep giving Cas weird looks when he says he's worried about the kids, and that maybe he doesn't want to loose them, because the others don't get that it would be loosing the kids. And if they think he's actually Jimmy who's taken back over the body and worried for the kids, they might put Cas in a new body far away and then put souls in the kids before he could get to them, so,,,, yeah. Running away. Defiantly the safest bet.
It takes a few years, of research and hiding out and following rumors and whispers of rare violence that could only be humans. He has no idea how to raise children- Souls don't really have children, even souls in child bodies are just small adults- and while Jack never seems to fully grasp that Cas isn't their dad, because he doesn't remember their dad, Claire does, and she screams and argues and fights and hits when she realises the thing in her dad isn't going to hit or scream of fight back.
But she never actually leaves him, because he made it very clear he's the only Soul that isn't going to turn her in, and he puts food on the table and a string of hotel room roofs over her head and keeps her in her own body... and sings her songs, and tell her stories about other worlds, and puts bandaid on her scratches and, and comforts her after nightmares, and acts like her dad, not like Jimmy, but like Cas thinks he is her dad.
She has her own issues with Jack, because he had no problem with Cas, but she'll side with him over Cas on just about anything, and Cas can't put his foot down half the time when he's out voted two-to-one on things, and like Democratic vote is how humans decide things, right???
Anyway several years and miles and miles of driving and hiking and following any lead they can, they end up in in front if a bunker in the middle of No Where, Kansas, where they finally, finally find humans.
And the really pretty one with all the freckles and the bright green eyes just keeps pointing his gun as Cas like he doesn't have kids behind him, what is wrong with this species!?!?!
And then Of course the only reason Cas isn't killed on the spot is because Jack and Claire push their way in front of him and 7 year old Jack calls him their dad, and 11 year old Claire screams she'll rat them all out if they kill him, she fucking will!
And then its just The Host, but gay with a Destiel ending, please someone who's read the host tell me you see the potential here!?!?
Or maybe it could be something like this in another version of Apocalypse World where the angels want Claire and Jack for Vessels, and Angel of Fuck-You-and-Your-God-Thursday continues his trend of exerting his free will to get these kids and his Angel warding magic knowledge to the human ristance.
Its just the perks of the Host is that Souls are chronically, criplinging gentle and kind, and I'm such a sucker for Gentle kind person x jade person with a traumatic history and issues that becomes soft because of the gentle soft person trope.
Plus if its in the host world, we'd definitely get Dean teaching Cas to shoot a gun, all "this is how you hold it" when his arms around Cas.
Also also if its Host world, Castiel's getting the AU name Casting Light Upon The Shadows, which Dean immediately shortens to Cas, and is never heard again, but I think it's a good name for how Soul names work in the Host
Jack and Claire defintly get to do some parent-trapping in either version cause they're not out here for that angsty pinning either, and Dean defiantly makes a cool dad.
Also host world offers domestic fluff shopping trip chapters, as society did not crumble, as they'd be running low on supplies and food, and Jack I've-never-read-a-room-in-my-life Kline just being like "why doesn't dad just go shopping? We went shopping all the time before we got here. I miss cereal." And Claire I-like-antaganizing-the-authorities Novak would be like "yeah, all you gotta do is put on sunglasses and like, act nice, or is that too much for y'all??"
So Dean tags along to make sure Cas doesn't do anything suspicious to signal the others souls
And maybe the nearest town is far away and it has to be an over night thing, and Cas gets them a hotel. Maybe there's not enough beds, who knows. ¯\_(ツ)_/¯
Really, I just have that specific imagine in my head, of Dean pissed and freaked out, pointing a gun and Castiel, where Castiel has little Claire and Jack behind him, and God if I had the patience I swear it would be such a good romance story.
Also, with the fact Souls are essentially immortal as long as they can keep transferring Hosts when one gets too old, Cas would have to come to terms with his mortality, and his choice to be essentially human, when probably isn't something that would have settled in untill he got to the Appalachians, as he'd had been too procured with the worry of getting thr kids there alive.
Also, fun fact, Jake Abel is in the host movie as the love interest... or not so fun fact cause that movie was so unfaithful to the book :|
Actually, speaking of Adam
Sam and Dean had had to abandon Adam way at the start of the invasion because he got captured, little do they know, Adam never went under, and over the years the Soul inside him, Michael, came to peace with their situation. They never went after the brother, of course, knowing they'd never believe Adam was still in there.
They practice and its a herculean effort, but they figure out how Adam can take control back of his body and they share well.
And fall in love of course ❤️
At some point I suppose, for some conflict, Sam gets captured, and a Soul placed in his head.
The human in the bunker scatter, and Dean's like impoding, so Cas admits he knows how to remove a Soul from a human host, and that if they find him, and Dean promises they'll send whatever Soul is in Sam safely to another planet, he'll do it.
And they and Claire and Jack go off on a road trip to find him. Starting at the hospital in the town where Sam was caught.
It's not actually hard, all Cas has to do is pretend to be a journalist wanted to speak with the soul that was placed in the body of host thats been in hiding all this time, for an article, and everyone just straight up tells them where they last saw that very tall, easily remebered, man.
They find him in Windom, Minnisota, because the soul in him wanted to be with "his brother", and that's where Adam and Michael have been living.
Well, Micheal and Adam are like, not chill with that, cause like, the Soul isn't Sam, and they don't know or trust this Soul- I guess this would be Lucifer, but like, it's not relevant and hes certainly not going to act like Lucifer ¯\_(ツ)_/¯- so they can't act like themselves in their own house, but they also can't kick him out because a Soul simply wouldn't do that under normal circumstances.
When Dean and Cas find them, they're like "Kay, guess we're rescuing Adam too, thats gonna be a fun conversation"
They break into the house in the middle of the night, leaving Claire and Jack in a hotel for the night, and they knocked Samifer out, easy peavey.
Adam and Michael put up a fight, and that surprised everyone, especially when Adam pulls a gun out, because Souls just like, don't? Do guns?
Everything come out and there's hugging and apologizing, and Yada Yada. Michael's like, "You really went and lived with them??? Like, I like this one (talking about Adam), but to be in the viper's pit???"
Cas is like "Yes, they are a strange species, very violent, but they tend to come around." Making heart eyes at Dean until Dean looks his way and he looks away quick.
Anyway, they remove the Soul from Sam, but not from Adam, and Sam wakes up an hour or so later, talking about how he's been screaming away in there, not letting the soul get any information out of his head. Except, the fact he has a brother slips through at one point and Sam had acted like he was thinking of Adam, so that's really why the soul had come to Michael and Adam, hopping to get more information out of Sam, by being around family.
After that, thinking about the unused, second cryotank sitting there, Cas pulls Dean into the hallways and makes a request. Dean had watched Cas perform the surgery on Sam. He knows how to do it, and he wanted him to do it to Cas, so Claire and Jack can have their Father back.
Maybe they go back and forth a bit, Dean won't admit his feelings, even to himself, but even if Claire and Jack should get they're dad back, Dean doesn't want to loose Cas, but Cas ultimately wins, and so, there's that angst.
Except, unlike Sam, Jimmy doesn't wake up. They wait all night, and we'll into the morning.
Dean's sitting on Adam and Michael's couch, holding Cas's cryotank in his lap just kind of blankly zoned out, coming to terms with his feelings for Cas now that it seems to late, when Claire goes from texted his phone- and Cas's, sitting there in the coffee table- to calling Dean, and Dean doesn't have a choice but to go get them, to explain what all happened.
Of course, Claire and Jack had known what Dean and Cas had been going to do for Sam, and Adam, and of course they'd thought about it, but in so far as they'd figured, they needed Cas, he couldn't just leave, and if they got him a new body, that was just another person all mixed up in everything. So they hadn't mentioned it.
But when they go inside the house, they see the cryotanks, and it's scary, because they know one of those is Cas, who's just as much their dad a Jimmy.
And you know, Claire might really, for the first time, have to come to terms with that herself, the familiar loving relationship she has with the otherworldly being that took her dad from her. A Dad she can barely remember at this point, who was more an idea than anything.
So they all hide out in Adam and Michael's house for a few days, untill they're really truly sure that Jimmy's not going to wake up. Claire and Jack have their proper, final good-bye to their dad, and Dean puts Cas back in his body.
Cas is beyond confused when he wakes again, but he gets the run down, and Dean finally confesses his love, and Cas confesses back and it's cute and sweet, and they kiiiiiissssss.
And Claire and Jack hug him, and tell him they're glad he's staying. meanwhile Adam and Michael are pushing them all out the door, like "sucked to see you, don't come back- and don't get caught or we'll make you regret it if Seekers come after us for this!"
But of course all three brothers had talked a lot over the week, and there's the underlying knowledge that if they ever really -like truly desperately, as a very last resort- needed anything, they can came ask Adam and Michael.
So they leave and Dean's like "so what planet do we send Sam's parasite to so he can't rat us out to anyone here?"
And Sam's like, "Which ones are the worst Cas? That guy was a dick, like constant mind games trying to get information out of me. Giant bag of dicks."
Cas, without missing a beat. "probably fire world, but it's closed from occupation due to the fact The Dragons' diet requires the murder of the planet's other sentient species. And it's not far enough anyway. The soul would be awake again within our lifetime, and interplanetary communication is almost instantaneous. We'd have a few decades at most."
And Sam's like "no, yeah, he was from there, that place looked terrifying in his memories. Thats why he's here, he enjoyed it, the fact it was murder. They made him leave for his own health. They didn't know the extent to how crazy he was, but he couldn't hide it completely."
"Oh great, so they sent him to the most emotionally termoilent of planets." Cas rolls his eyes. "Maybe a lifetime as a seaweed at the bottom of the ocean would do him better. Certainly the hivemind will keep him in line."
And so they drop Lucifer off at the shuttle station, in the loading bay for the Planet of the Seaweeds, and never look back.
They decide to go back to the Bunker, see if anyone came back, human or soul, and go from there, trying to relocate and/or rescue their family.