Disclaimer: I don't own Buffy or Kingdom Hearts. This story was written for fun, not profit.
I have no idea where this particular piece of crack came from. It's set pre-KH1 and post-"The Gift" and it assumes some basic knowledge about who (what) Dawn is. I promise it makes absolutely no sense whatsoever.
The first time Dawn Summers sees the little black shadows, she doubles over and throws up.
It's such a stupid reaction, because they're little and pudgy and cute - "it's like kicking an evil puppy," Willow says - and there's something clumsy about their mindless grasping. No one else is terribly concerned, not when the squirming things are so easy to kill. There's no aiming needed. Just point the crossbow and shoot.
By day two they've been officially dubbed evil puppies, although Xander likes cockroaches better and makes half-hearted jokes about Raid. Dawn can't correct him. Her mouth's too full of bile and green light.
On day three the power starts going out and the radio stations play evacuation instructions nonstop. Cleveland's still mostly clear and so are parts of Los Angeles - because of the demons, Cordelia says before the phones tie up completely, because some demons don't have hearts and souls and even they're running scared.
Dawn helps Giles tear through their reseach books, and she holds the supplies while Tara and Willow ward everything like that will make a difference. There's other little shadows now - flying things stuffed full of magic and huge round creatures for breaking down walls and long-limbed marionette-soldiers that bobble through the streets. When they scuttle by she crouches out of sight beneath the windowsills and chokes on thin air.
They sound like empty places and rushing wind - like the ragged edges of the hole in the world.
When Xander doesn't come back on day five, she knows deep down in her bones that there's no point looking for him.
Big open hearts are like magnets for the squirming things, their food and water and sunshine - but she stands aloof from the others with her hands curled up in helpless fists, and she doesn't say this.
Every night she stands with her arms in front of her and tries to close the hole with her own two hands. It never works and she never hopes it does. Keys can't lock things all by themselves.
But she has to try. Her sister told her to live, and that promise is the only piece of the world the grasping shadows can't reach.
"They're Heartless," she says three days later, when it's her and Giles and Spike, because she's seen what's left of Willow and Tara, and Anya would've been back by now if she were still alive.
Giles just looks at her, like he's taking in her secondhand genes and the circles under her eyes and how she can never be what her sister was, she can never save the world with her own two hands. "You know what these are?"
She closes her eyes and sees stars pop-fizzing and winking out like Christmas-tree lights. "Yeah. I do."
"And you couldn't've said so sooner?" That's Spike holding his last cup of blood from the cooler, which is the least of her concerns.
"I didn't know I knew," she says. "I think it's a Key thing." Maybe she ought to be ethereal and otherworldly (and isn't that what she is?) but she's tired and hungry and there's a giant icky bloodstain on her jeans. "Doesn't matter. They aren't in any books."
Spike looks like he wants to throttle her more than usual. "So how do we kill them?"
She doesn't snap her eyes open or anything, because she's not that melodramatic.
"You don't," she says.
When she's half-asleep and hot and smelly and lost in a haze of petulant exhaustion, she wonders if there's a matched-set deal she's missing out on. She's a Key (and this is important; it matters like Buffy's Slayer-dreams, it matters in ways that make hellgods look tiny and she doesn't know why) and it stands to reason that there has to be a Lock somewhere out there. If she's the way to open the world, there has to be a way to stopper it up.
Once she thinks that maybe the Key and the Lock are all destined and star-crossed and crap like that, which is about when she realizes she's going completely fucking bonkers.
Day eleven starts with weird swirly darkness eating up the sun and knotting up the ground. She steals Spike's big broody creature-of-the-night duster and wraps Giles's scarf around her neck - not like they need them now - and slips outside, and now she doesn't even have to stand still to hear the world rupturing under her. What's left of Sunnydale is blurring and cracking at the edges.
Her mom and Buffy had the right idea, getting out when they had the chance.
She lets the duster's sleeves fall over her hands and looks up at what's left of the sky - won't be long now - and utterly fails to think up anything deep and meaningful. Mostly she hopes that she doesn't show up in the afterlife in Buffy's old jeans, because they're ruined.
There's no lock, just a Keyhole. She stuffs her hands in the duster's pockets and scowls up at it, and she can't even say that she's the last person left in the whole world - because there's green light all through her now, which probably means she isn't a person at all.
When her world breaks apart, she balances on a little piece of asphalt and dirt with a crossbow in her hand, and she lands between stone buildings with her feet on the ground.
Her sister told her to live, so she does. Simple as that.
Traverse Town's schoolteacher is tall and brunette and an oldtimer - ten years and counting. The sign on her little brick building informs passers-by that no, she won't be inviting them in anytime soon.
A couple times a day she stops mid-sentence and tilts her head at the sky, and then she sets her lips in a thin line and grits her teeth and goes back to teaching mathematics on a patched-together blackboard. This is how her students know another star has gone out.
Every one of them says Miss Dawnie can hear the Heartless.
She wishes they were wrong.