There could be three ways to do this:

The first two have more or less the same trope = (post-movie) Natural Portal Shenanigans make either Danny or Astro cross dimension and Astro has Toby's ghost following him along for fun and only Danny can see him because he's an halfa.

The third take is the Fusion AU =

Danny as Toby dies in the same canonical accident, but the two cores instead of blue and red are green and pink/magenta ( ͡° ͜ʖ ͡°).

Phantom as Astro. In this Danny and Phantom are two different persons, but instead of "normal" superpowers/weapons, he's half-robot/half-ectoplasm entity (it's different than being a ghost, I still stan that ghosts are the post-mortem manifestation of the deceased's soul and you can pry this from my specter's cold hands) (Meaning: Phantom is not Danny's ghost in this).

Jack and Maddie as Dr. Tenma. They form an amazing team and something so trivial as an absentee single parent in Astro Boy canon won't stop me.

Frostbite as Dr. Elefun. I contemplated briefly Clockwork for this part, but the "supportive wise mentor" fit better with our favorite Yeti than with our cryptid stopwatch, not counting that he has already medical and technological knowledge in DP.

Jazz as Orrin (the robot housekeeper)? This one doesn't fit as well as the rest of the cast, so maybe there's no Jazz or she's in another city as studying-abroad-big-sister.

Sam as Cora. Rebellious girl with wealthy parents, who fights for her rights? Sign her in. (Not counting the teased romance between her and Astro/Phantom, that's only a plus.)

Tucker as "himself" (AKA not any particular role, just one of the orphans of the Surface). Techno-Geek that repairs robots for the Robot Fights and bonds spectacularly with Phantom.

Dani as ZOG. I know it's strange, but hear me out: ZOG was revived by Astro's core and it still keeps part of that energy, making it virtually both Astro's sibling and child! Ring a bell? Plus ZOG is a little shit when it's able to, so it's only a natural decision, really! (≧∇≦)

Cujo as Trashcan. Yep, the trashcan dog deserves the puppy counterpart.

Now that should be everyone! ...Or should it? Oh! Right! The Villains:

Freakshow as Hamegg. Who would be a better showman/ringleader than the insane circus owner who controls robots ghosts?

Vlad Masters as President Stone. Of course it was going to be him. Old friend of the protagonist's father? Check. Power hungry? Check. Wants the protagonist for one of his machinations? Triple check.

Plasmius as Peacekeeper. Pink/Magenta core explained! Who would have thought about that? (≧∇≦)

Skulker as General Heckler. Vlad's second in command and enforcer of his commands, it feels only natural.

There are so many other characters to assign, though at the moment I can't come up with what to do with the robot trio of the Robot Revolutionary Front or Valerie Gray, but this discourse made me want to re-watch the movie, so I'll probably add something tomorrow.

Emmet tried his best to keep his smile on his face and to not scowl in the direction of the Memory Fiend. By all means, the man was actually pleasant to talk to, highly optimistic, and verbose even- in a way that pinched at Emmet’s heart. Memory hadn’t done exactly anything worthy of scorn.

Besides having been born a Devil that was.

Emmet didn’t even want to work with the Fiend. Yup! The very thought made him genuinely sick to his stomach.

It wasn’t exactly as though he had a choice.

See, the thing about Emmet’s unfortunate choice in career was that he never wanted to become a Devil Hunter. Nope. Nothing about the profession interested him and he was even verrry squeamish at the beginning. He got over it. Before all of this, he was a subway conductor and quite happy being so as well.

But Emmet had to be a Devil Hunter you see. Because he had to avenge Ingo. His twin who had been killed at the hands of a Train Devil.

Ironic. Wasn’t it?

That day... he didn't like thinking about it. Of course, Emmet knew that there was a Devil for every fear on the great blue Earth they called home. But... it just never really occurred to him that people would truly fear trains considering how much he and his brother adored them so much.

That was his mistake.

Emmet hadn't even gone to work that day. He had gotten sick, yup, and took sick leave. Ingo did go to work. He did not come home.

All he could remember was sitting in his apartment, laying on his couch as he nursed a cup of ginger tea when the reports that Gear Station had been utterly and entirely destroyed by the presence of the Train Devil came in.

His mug crashed onto the ground. It was a nice mug and a nice rug that stained after Emmet ignored the spill and raced out of his apartment, fighting past the dizzy spell that threatened to overcome him in a desperate attempt to reach his twin.

By the time he made it to the station, it was too late. Everyone was already dead.

Ingo was dead.

The rubble caused in the aftermath was so great that he couldn't even retrieve his body to bury. Standard procedure when it came to the disaster that Devils created.

It was hardly a question about whether or not Emmet would switch tracks and become a Devil Hunter himself.

He worked in the Private Sector. Emmet did not want to work with Public Safety, nope. After all, he blamed them inherently for their failure to respond in time to the Train Devil. What was the point of having special division headquarters in every city or town in Unova if they were so slow? Delays of that nature were despicable and unforgivable.

Emmet could do better on his own by collecting bounties. And he did, yup. He was practically the best Private Devil Hunter in the region because Emmet liked to win, and ever since a Devil dared to kill his brother he had declared his own personal war against the disgusting monsters.

Elesa didn't agree with his decision and attempted to get him to work under her in Public Safety. Emmet refused. They had a falling out.

He had thrown some verrry not nice accusations at her. She had every right to consider their friendship done and over like Emmet did but...

("Here," she said, handing over a bundle of clothes.

Emmet wasn't expecting to ever see her again after cutting ties. Especially not in front of his apartment door in the middle of a rainstorm.

But there she was, soaked to the bone in her nice black and white suit, with her makeup slightly runny. From the rain or her tears, he couldn't figure out.

He was still a bundle of righteous fury, even weeks after Ingo's death and days after burying an empty casket, but he still took the offering and said, "I am Emmet. What is this?"

"A uniform. Since you're a Devil Hunter now," she answered.

Emmet narrowed his eyes, "Private Hunters don't have to wear uniforms. And you already know my opinion about Public Safety."

Part of him was glad that she still felt comfortable rolling her eyes at him, because their last meeting had left her quite rattled, "I know. Trust me, I do. But our uniforms are reinforced to take beatings from Devils. Normal clothes aren't. So I personally commissioned those for you."

Still wary, he unfolded the top layer. It was a great overcoat, purely white with large cuffs and a flared bottom. Just feeling around he could feel some sort of flexible bone structure woven into the material, likely to give it that shape.

"One of a kind," Elesa said, eyes sad. "I know... I'm probably the last one you wanted to see. But I would hate myself forever if I didn't make sure that you didn't end up killing yourself in this stupid crusade of yours."

Emmet folded the coat. He didn't say anything to her.

She sighed. "Yeah. Well. I delivered it. That's what I came here to do after all."

Elesa turned away and started to walk down the end of the hall, and just as Emmet was ready to close the door she spoke up one last time.

"Love you," she whispered. "And stay safe. If not for me, then for Ingo.")

One of a kind his ass.

If it was really one of a kind then the Memory Fiend wouldn't be wearing the same exact outfit but in black.

Emmet hated that. He did. Why was he matching with this Devil that had been forced upon him? There was only one person in the entire world that he was supposed to look identical to and that was his brother.

At least the Memory Fiend had no face. Just a swirl of scar tissue. And an ever-present smile that was barely a smile at all. Not like Emmet's smile. His, while forced and barely truthful, looked right on his face.

Memory's smile looked as if someone was pushing up the edges of a frown.

Emmet hated how much that reminded him even more of Ingo too.

Another difference between the two was that the Memory Fiend wore a sort of diving helmet to cover his head. Emmet did not know if it was purely for easthetic or what but at least it ensured that no one would confuse the two from just their coats.

Well, as much as he disliked Elesa for lying to him about the coat, he did have to admit that it got the job done and even elevated him amongst the other Private Devil Hunters. Not many had the resources that Emmet had to get clothing that would protect them instead of the flimsy fabrics that most wore.

And it would have been absurd to wear white when tracking down and killing those blood-ravenous beasts on any other person but not on Emmet. His coat was still as pristine as the day he got it.

Part of that was due to his natural skill in avoiding attacks and carnage, and also due to the many Devil contracts that he had.

He still greatly despised Devils, do not get him wrong. But contracts were of the essence if he was going to continue his job to ensure the safety of all passengers. If Emmet wanted to make sure that everyone's loved ones got home after their commute-

(Unlike Ingo who never made it home.)

-then he would have to be the verrry best Devil Hunter there was. And that meant making deals with some of the lesser Devils who were willing to work with humans so as to not get killed in exchange.

Multiple contracts with Devils were pretty unheard of. And also somewhat frowned upon. Emmet did not care! Nope! He had a contract with the Eel Devil and the Spider Devil.

All that he had to give in response to calling upon their aid was blood from his arm- the Eel Devil liked to feast on him that way- and house some offspring of the Spider Devil in his house.

He shivered thinking about how exactly it was that the Spider Devil made babies. As far as he knew, Devils couldn't copulate as humans could. Emmet was hoping that they were just random spiders and not mini-clones of the Spider Devil. Yuck.

His skill, his uniform, and his contracts- those were what made Emmet the strongest Private Sector Devil Hunter in Unova.

And apparently also why he caught the attention of Public Safety. So much so that they even loaned him one of their Fiends.

Before crossing the platform to his connecting train, Emmet knew very little about Devils other than they were terrorizing the world. He learned more on the job.

Devils were easy to understand and he had heard whispers about people who were considered Hybrids; humans with the ability to turn into Devil forms.

Devils were usually born from the fears of humans, however ridiculous those fears may wind up being. If enough humans feared it, there was a Devil for it. Spawned in Hell, upon death brought onto Earth, and upon death again brought right back to Hell. A seemingly never-ending cycle that just went on and on.

Emmet doesn't even want to think about how many times he had been contracted to kill the Rat Devil. It was even worse than the rats they used to have in the subway.

Devils. Hybrids. Fiends.

The concept of Fiends was pretty well known in the hunting circles. And when Emmet found out he had spent an hour or so clutching onto the bowl of his toilet after emptying his stomach.

Apparently, if a Devil was weakened enough- on the verge of death, as it was- and there was a human corpse laying around then they could possess it. The original human would have been dead and gone by then, usually, so nothing but the Devil would remain.

That was why Emmet did not want to work with any Fiend. He did not want to have to stand next to a Devil parading itself in a carcass as though the body belonged to them.

But the League of Public Safety seemed to think otherwise. And now no matter how hard he tried to lose the Memory Fiend he just kept. Following. Emmet.

And since Public Safety wouldn't take him back, it was up to Emmet to attempt to ward off the Fiend. His current plan was to annoy and belittle him so much that he abandoned his post, which would be considered a betrayal of his agreement to work with Public Safety meaning Emmet could legally get rid of him.

Said plan was not working so well.

"You must have been a verrry weak Devil," Emmet stated, voice tense and on the verge of snapping in anger. "Yup! Had you not gotten to that body first I would have killed you myself!"

"I have no doubts about that!" Another thing about the Memory Fiend was that he was loud. No sense of volume control at all. Emmet couldn't tell if that was just a part of the Devil or an aspect of the body it was possessing. "You are quite the talented Devil Hunter after all!"

How was it that the Fiend didn't balk at the unhidden and open death threat? Emmet didn't get him and didn't want to either.

"I mean," he tried again. "Who in their right mind would fear memory? Those are the kind of things that people love and cherish. Unlike you. I don't think anyone could love a Devil. Nope!"

"You'd be surprised," Memory commented, and Emmet's chest puffed up as he was about to laugh viciously at the idea of a human loving a Devil, but when the Fiend continued he realized he was mistaken about what part he was responding to, "More people fear memory than anything else."

Emmet stopped walking. "What do you mean?"

"People are afraid to lose their memories, for one," the Fiend tilted his head at him. "And simultaneously afraid that other people will forget them in turn. These are quite common fears that every human experiences at least once."

He... couldn't deny that. That was why stories about amnesia and memory loss were so rampant in the media. Memories were what made people who they are. To lose that...

"For example, I know you are afraid that one day you will forget the sound of your twin's voice."

Liquid fury soared through his veins as Emmet saw red, "How dare-"

Memory continued, blithely ignoring him, "As the Memory Devil, I am called to near constantly. Memory is as present a human aspect as emotions are. People remember things every day. They also forget things too. At my peak, I was able to see into every human's brain and recall all their most pleasant memories and their worst. Bad memories always tasted the most delicious, with the amount of suffering that was weaved into them."

"Well, that peak must have been quite short," Emmet spat. "Considering that you were forced to take shelter in the body of a human corpse."

Memory Fiend tilted his head at him. "Oh. You think that I had the choice between life or death when it came to taking over this body, don't you?"

He stilled. "Isn't that how all Fiends come to be?"

"For others maybe," and it was about the first time that Emmet felt that the Devil's smile was genuinely cruel. "Not me."

"Then why would you choose to weaken yourself by inhabiting a human body," Emmet demanded, wanting to know the answer.

"Because for the first time in my existence on this Earth, away from the comforting chaos of Hell, a human's cherished memories tasted like ambrosia to me," the Memory Fiend placed a hand above his body's heart. "My body, he was dying. A lot of people were dying. I have heard humans say that their lives flash before their eyes upon the verge of death, and it's true. Whenever there's a congregation of mewling pitiful humans having their lives snuffed out by fellow Devils, it is like a Church bell crooning in my mind, and I hurry towards the sound. So many recollections, surging forth at once while the new memories of the pain and torture that they were in were forming."

"Like a banquet," Emmet commented, disturbed. "Or an all-you-can-eat buffet."

"Exactly," Memory Fiend smirked. Emmet did not like the expression on that face. It slipped off his face into something brimming with adoration, and somehow that was even more sickening. "But him. His memories... the second I saw them, I knew I had to have them. In a way that I had never had a human's precious moments before."

Then, the Memory Fiend looked at him, and even with the upper half of his face missing- Fiends always seemed to have some aberration on their head, which denoted them as different than Devils and presumably Hybrids- he looked upon Emmet as though he knew something that he didn't.

Emmet did not trust that look. He did not trust that Devil.

He took a step back. And then another.

The mood suddenly switched as Memory perked up, and a surge of a desperate need to breathe washed over Emmet, as he had been unaware that his lungs were tight and restricted during the interaction. "I think I can hear the Pigeon Devil up ahead. If you want to prevent any more humans from dying we better get a move on."

"Yes, I am Emmet, I agree," Emmet forced out of his mouth, grateful that the conversation would be over. It was unpleasant, yup, he did not want a repeat of the unspeakable horrors that the Fiend had confided in him. Not when he couldn't put him down like a dog for it.

"Oh, one more thing," Memory said, and Emmet was really tired of hearing the Devil run his mouth. "Before you get any misconceptions, my body actually made a contract with me before he died."

What?

What... was he implying by that.

Emmet wisely chose not to question him, not sure if he even wanted to know the answer, and the Memory Fiend sauntered past him on the sidewalk.

She is the only home he knows now. The only ground he can count on. The only safe place to rest his head.

How long has it been since they’ve heard music?

When the wars ended, girls in pretty dresses danced and sang, and everyone waved their flags?

When Papa took them to the opera and they fidgeted in their seats, trying to play games without getting caught?

When Arthur took them to see a famous singer or two, and they started to see what all the fuss was about?

It’s been so long since they heard music. Not a single, lonesome melody. The black didn’t provide much as far as records, radios, and mp3s go. All they had were their own voices out here, the echo swallowed by the stars.

Amelia would sing, sometimes, on the ship. He knew it. In the lone hours of the morning when she thought no one could hear her, she would sing Serenity to sleep. The witching hour when the nightmares and all-too-real-mares kept her awake.

The witching hour, when all the best witches were up.

A man in a brown jacket and sash comes to dance with her, and a smile holds her up, as if pulled on strings, pulling her back, back, tethering her to a time when she was an eager-to-please American girl. Well, no, not quite. There was something fake there, then. Something plastered on. This isn’t made of stitches, and glue, and expectations.

This is America.

This is free.

A smile begins to break across the Canadian’s face too, like all the masks they’ve put on—(and there are many layers to get through)—are cracking, and for a brief moment she is America again, and he is Canada, and it’s them against a world that still exists.

Wild thing. Wild, wild girl.

She didn’t like being caged. Didn’t deserve it. Being cooped up in a tin can hurtling through nothing but the dark, gravity a distant memory. She didn’t like being away from her land.

None of them did. It felt like taking a drug you’re allergic too—not allergic enough to stop breathing, but allergic enough to never feel right, to always feel a little sick, so long as you take it. And she wasn’t the only one who had bouts of not-quite-sanity because of it.

How long has it been since they’ve been out?

The others went on missions—(a funny image: the Nations of the earth, stealing from the very people they once called their own, once called themselves, in order to survive…what a sorry lot they were). But the Captain regarded America as a bomb two ticks from going off; he didn’t dare think that going out planetside would bring her back down to, well…Earth. Or what passes for it these days.

It is at this point that she catches sight of her brother, standing out in the grass—so much greener when your world has been grey for so long. Those eyes, glittering, reflecting the sky—blue here, now, not black and white…(Dorothy, do you think we’re back in Kansas now?)—that smile is for him now. It makes her face shine, and he doesn’t think he deserves that smile, this golden girl…

…How long had it been since he last saw her smile? Really smile. Not an ignorant, or a plastered, or a not-quite-sane smile, but really truly smile?

It always seemed to go back to wars ending. A nice president maybe. No personal happiness. Just that of the world, and being told we can stop fighting our friends now. We can stop fighting…because we made them too weak to stand.

Was there anything personal to speak of?

England and her remembering, in a house in the moors, like a childhood dream, they still cared about each other.

Papa and her baking pastries. Matthew and her eating them all by themselves.

There was them. Her and Arthur. Her and Francis. Her and…him.

They all smiled before. She smiled.

He has a photograph from some year starting with nineteen where he managed to get that million-dollar-sighting, of his million-dollar-girl, and that more-than-a-million-dollar smile. A gentle, flickering thing, like catching a sunbeam with a net.

She smiled when they ran into the forest at their borders, smoking weed, stealing moonshine, running from the rest of the world, and all their bottled happiness.

Whenever their world was about something greater than pursuing happiness…that’s when they seemed to find it.

But you can’t chase a negative, can you? And we always must be chasing something. So let’s chase a smile all the same.

They were children once. Before all the wars and all the victories. Before they needed herb and liquor to laugh. Before they were used up, stripped for their parts, they and their people shipped out, the address on the box a blot of ink.

“We’re in trouble!” a little golden head pops out from behind the coffee table.

Matthew continues writing.

“We got cut off!” she gets closer.

“Cut off? Cut off from what?” he asks with the air of someone who isn’t really paying attention.

“Our platoon, Matthew!” she says like they’d been over this a hundred times. “We got outflanked by the independent squad and now we’re never gonna make it back to our platoon.”

He doesn’t respond.

“We need to resort to cannibalism.”

Matthew still doesn’t look up, unfazed by the should-be-alarming phrase, as if they resort to cannibalism every other day.

“That was fast,” is all he says. Like the only difference from all the other times is it took longer before. “Don’t we have any rations or anything?”

“They got lost. We’re gonna have to eat the men.”

Matthew looks up now, impatience leaking into his tone. “Aren’t you supposed to be practicing for your dance recital?”

She pouts.“I can’t practice without a partner…But maybe…if a kind nation were to offer his help…” she twirls her hair, trying to make herself look like the pretty girls in the books and paintings.

“Papa’s in the other room.” He flicks his pen in that direction.

She jumps up on the couch like a cat, swiping the notebook out of his hands with the same air—

“Amelia—!”

“Dance with me!”

The Great White North blinks up at his sister.

They are small. So small they could follow foxes into their dens, and fit into hollowed out trees in neverlands.

He glares at her. “No,” he picks up the the book, brushing it off. “I need to work on this.”

“You can work on that tomooorow.” She puts her chin on his knee and blinks, giving him those puppy-dog eyes. “don’t you love me?”

He lifts up his knee, trying to get her away. “No, you’re the worst.” He says, sounding very much like a nine-year-old boy.

She starts crying, like any self-respecting nine-year-old girl should.

At this he casts the notebook away, looking at her with pleading eyes “Wait—no! I didn’t mean it! It was just a joke!”

“Mon dieu!” Francis deigns this as the moment to walk into the room. “Whatever is the matter mon petit cheri?”

“Matthew won’t dance with me!” she points accusingly at him, her other hand rubbing her eye.

“Aww...But, my dear, is that a crime?”

Amelia pauses, thinks for a second. Matthew can almost see the gears turning in her head. “Yes! I heard the king say so!”

“Is that so?”

“Yes! He said ‘by my decree, all brothers must dance with their sisters’!”

“Well, if the king said so, then there isn’t much I can do, is there?”

“But Papa!” Matthew stands to protest.

France is already setting the needle down on the old record on the desk. Amelia holds out her hand, smirking, checkmate, written in her eyes.

Matthew snorts, taking her hand.

They were children once. And she smiled, and she danced, and she joked, and she cried and made up laws to get what she wanted.

They were children once. They were happy once.

But that was before. Before the world burned, and the sky turned black. That was before the Academy broke her into bits and made weapons out of the pieces.

Now dancing, music, Earth, happiness, are distant memories. A memory within a memory, until you can’t remember what’s the dream and what’s real, if you made it all up, and what’s your dream, after all.

They were children once. But they grew up, and the earth got used up. And they traded their souls for smiles in dark alleyways and cramped quarters.

She looks so small. So weak. Sitting in the cargo hold of some ship with a name like ‘Dauntless’ or ‘S.S. Elizabeth’—(they all hated people who gave unbreathing things names that breathed). So small. But no trees and fox dens to hide in this time. Just a room full of boxed-up lives, in this purring, creaking bus, taking them to new universes where the grass wasn’t greener.

Their governments provided nothing but the best for their nations’ transport to new worlds. But they could never understand what it’s like to be ripped from yourself. And people could get insensitive at even the best of parties.

So small. Nineteen-but-not-nineteen-years-old, and she looks like she hasn’t eaten in months—(though he has eye-witness accounts that she ate more than one burger in the same sitting a few days ago). Her dress, hanging off her, bones that look like they could snap at any moment. She shivers.

They all look like this; like they’ve been used up.

They say it will be better, out there. Americans will be American on other Americas, and Canadians will be Canadian on other…well, you get the gist. But they know that while their people keep them alive, and their land keeps them alive, because it’s still there…their land is still there. America will always be America, on Earth, Canada will always be Canada…and these are just distant moons, and half-baked dreams.

And they will always only be half-alive now.

She asked them once, she asked them with a child-like yearning in her eyes, and a woman’s anger in her closed fists, if they would die. If, when their feet left their ground, they’d just float away. If this was what dying felt like, and they’d all been fading for a long time now.

Father said he didn’t know. That he hoped not.

Papa said softly that it might be better if they did.

And Matthew said if they did, they would die together.

So now she’s here, worse than dead; undead. A zombie, shaking in the cargo hold of some ill-named ship, because some politician said something stupid—like most of them do.

“Great party, huh?” Matthew spits as he rounds the corner.

Amelia looks up, then puts her head back on her knees. “Great party.” She repeats in the same tone.

“Good cake though,” he offers her the plate he brought from upstairs.

She blinks up at him, then shakes her head and lowers it again.

He sets the cake down on a nearby box.

“Dance with me.” He holds out his hand.

“W-What?” There’s something real in her eyes when she looks up.

“Amelia Jones, may I have the pleasure of dancing with you?”

She rolls her eyes. “There’s no music…Idiot.”

“Then…I’ll sing for you.” He swings back and forth on the rails.

“Really? You? Last time you sang it sounded like a dying cat.”

It’s his turn to roll his eyes.

“Come on.” He holds out his hand. “Do you have any other plans?”

She takes a deep breath and stands. He puts one hand on her waist, the other on her shoulder. Her head falls easily on his shoulder, like it took all her effort just to hold it up, and he’s the last safe bit of land that hasn’t been taken from her.

And he sings a new song:

“Take my love

“‘Take my land

“Take me where I cannot stand.

“I don’t care, I’m still free

“You can’t take the sky from me.

“Take me out

“To the black

“Tell ‘em I ain’t coming back

“Burn the land

“And boil the sea

“You can’t take the sky from me”

And she cries.

They were children once. They grew up once. And they were used up, once. And all it takes is once to make it hard to smile, hard to dance, hard to sing, hard to find any solid ground to stand on, to hold on to.

But not today. Today is different. Today she’s found ground. Today she can dance. Today she can smile. And maybe, just maybe, things will be okay.

She holds out her hand to him, Come dance with me! written into her features, and he moves forward to join her—

And the black comes crashing back, pulled over his head.