Author's Notes:

Well, here we are, yet another story from me. One of these days I'll finish one before moving onto the next.
I figure at this point, a quick explanation of something in the story is needed here, namely, what an Arcology is - I've no doubt a good number of people don't know.
As I know it, an Arcology is essentially a city that grew upwards in a single tower, instead of outwards. A self contained city, all in one massive tower. Now you know.
Explanation over... this is my first Kingdom Hearts story, focused mainly on Sora. Considering I've only ever played one of the Kingdom Hearts games (Chain of Memories, and never got far at that) this is likely to have a few potential mistakes in here and there. However, with the help of someone who's a lot more knowledgeable than I, hopefully you'll miss most of it before it gets here.

Right, enough rambling with me, on with the story - Enjoy!

There is a place, where the sun no longer shines. A place where things change on a whim. A place too dark for even the smallest glimmer of hope to survive.
There is a place that people go. They say that no one ever returns from it. They say it is impossible. They also say great wonders can be found there. They say they are protected and hoarded by those who hold sway there.
They call it The Dark Arcology. It is said to appear and disappear in a seemingly random pattern. No one knows why. No one knows where it will be next. No one knows how to attract it.
The Dark Arcology comes and goes, seemingly as it pleases. Every time, someone disappears from the world to be taken into it's grasp. They are never seen, or heard, or even felt again. To the rest of the world they are gone. They are no more. Missing. Taken. Lost.
Why? No one knows. When will it stop?
When will it stop?
When will it st...

"When will it stop?"
"Sora? Sora! Get up you great lout, you're dreaming again!"
Sora sat bolt upright, looking around quickly trying to get a hold of himself. Donald was hovering over him. He felt... afraid. Him? Afraid? How often did that happen?
"That was some dream," he breathed.
"You kept shouting 'When will it stop' in your sleep."
"I was?"
"Just what were you dreaming about?"
"I dunno... some dark building thing. Seemed like it was calling me to it."
"Another adventure?"
"Not one I wanna go on, it felt..." he paused, unable to find the words instantly. The feelings he'd had from the dream welled up, making him shiver involuntarily. "Unpleasant," he finally finished.
"You don't want to go? That's not like you."
"Let it lie," he insisted, not feeling it. Something still nagged at his conscious. "Lets go back to sleep."
"You're gonna dream again," Donald warned.
"I'll be ready for it this time," he smirked back.

The Dark Arcology loomed. It stood atop the hill, reaching into the sky, clawing at it, disappearing into the ominously dark clouds brooding high above.
He stood on another hill, the wind tugging at him, pulling toward the tower. It tugged on him, his clothes, his very soul. It called.
Come to us.
Come with us.
He took an involuntary step back, glancing at the sleeping forms of Donald and Goofy laying nearby.
Leave them. They are of no matter.
You alone are the keyblade master.
You could be much more.
Come to us, with us.
We can help you.
Unsteadily but warily, he started along the path to the Dark Arcology. The air grew colder as he approached, things seeming to become darker around him.
He glanced back again at his friends.
You'll see them again. Have no worries... trust us.
Though there was no voice speaking, upon hearing these words, doubt seemed to fade from him with the last of the light. The Dark Arcology loomed directly in front of him. Dark wasn't just the name of the tower, it was the description. It wasn't just black, it was beyond black, a black so black it looked blue. The lone entrance in the giant wall facing him seemed to suck at the eyes, giving the impression that if you looked too long, your eyes would be taken from you.
Come to us. Step through. We are waiting.
All doubts banished, he stepped through, vanishing from the view of anyone who might have been watching. The clouds sparked with lightning, rolling thunder. The sparking and thundering rolled down the tower, spinning a spider's web of lightning. With a final flash running back up the tower from the ground, lighting all the darkened windows briefly, the tower and clouds vanished with a loud crack, and a rush of strong winds pushing away from where it had been, flattening the grass downwards and away from the source.
No one noticed. Sora was taken, and no one knew what had taken him, or where.

"Welcome, Sora," a voice up ahead called to him. "Come on here."
The corridor wasn't as dark as outside, but it was still dark. An orange light glowed from the end, shadows playing across what could be seen.
The room at the end was roughly square, and had no apparent source of light. It was as if the entire room was the source.
There was nothing in the room besides him, with the exception of one desk, one chair, one door and one woman. She sat on the chair, at the desk, with the door behind her. With a sucking sound, the way he'd come in vanished, blank wall replacing it. He almost started to it, but the woman spoke.
"Don't be alarmed, Sora. You've nothing to fear here."
"But... the door-"
"Don't let it alarm you."
He turned back to look at her. She wore white. It seemed out of place somehow. A white shirt, a white jacket. Her hair too was white, long and streaming down her back, though her face showed no sign of age. She looked older than him, but only by a few years.
Her eyes though, twin black holes, all of them. They too sucked at the eyes. Without them, he would have called her attractive.
She smiled at him, and waved a hand absently. A second chair faded into existence opposite her, and he found himself sitting down without even thinking about it.
"Who are you," he wanted to ask, but somehow it came out as, "What are you?"
"You don't need to know that. You only need to know you have a choice standing before you."
"What choice?"
"You can join us willingly... or unwillingly."
"The difference?"
"How well you are treated."
"What do I gain from joining you?"
"What's the catch?"
"That's all?"
"Your loyalty to us, to what you are ordered to do, to what we tell you, and to nothing else."
"But... my friends-"
"Are of no interest to us, and in joining us, you give them up for our friendship. Two friends? Here you will have far more powerful friends. Ones who will be as loyal to you, as you are to us. Or if such is your wish, you may choose which of them you want."
"I choose my friends."
"You cannot."
"Why not? I want them with me."
"The offer is not extended to them."
"Then extend it!" he shouted back, irritated at the complete lack of any change in this woman. Her expression never changed, always calm.
"That is not in our interests. However, take our offer, and when you attain rank within our system, you'll be able to recommend them. Such is as it was for you."
"Who recommended me? Who did you con into working for you?"
"We did not con anyone. Seifer joined us of his own free will."
"Seifer? Why would he join..."
"He was interested in our offer. Now tell me honestly, Sora. Will you be a willing taker, or an unwilling taker?"
He looked back sharply with a defiant expression. "Neither. I don't want a part of this, I don't want your offer, and I'll fight you if I have to."
"You have no choice, and no chance. You will join us, one way or the other. There is no escape once you have been selected. You cannot fight us. You cannot match the power we offer without the power itself, and we do not tolerate disobedience or treachery within the ranks."
"I'll have no part of it! Let me out of here... or I'll fight you anyway!" He pushed the chair back, the keyblade appeared in his hand at these words, ready for action.
She simply laughed at him, a short, harsh, scornful laugh. Then she too stood, the table and chairs fading out.
"You don't get it, Keyblade Master. You have no choice. You will join us, or you will be forced into joining us. There is no other option."
"And if I fight?"
"You will lose."
"If I did?"
"Don't be silly. Keyblade Master or not, you stand no chance against us."
"We'll see about that!"
He took a swing at her, but it didn't connect. She vanished before it ever reached him, and reappeared again after it had passed her.
"You cannot defeat me. It is impossible."
"There has to be another choice."
"Is that so? Then I shall offer one." She turned and tapped the door. It blurred, shimmered, then seemed to split into two identical doors, side by side. "One door will lead you along the path to willingly working for us. The other... leads to many places, only one part of which will lead you to the way out. Choose."
"It's a trick."
"I will allow you a look through each door."
"Open them both, I'll look from here. No tricks."
"You are a cunning as you are reputed to be. Very well." A snap of her fingers and they both opened. The left door showed another room, another desk, and another woman. The other had stairs leading downwards. Screams echoed up from it. It sounded like people being tortured.
"This is my choice?"
"It is quite clear which leads to what. There is more there than what you hear. There is an exit there. None have ever found it."
"I will."
"You plan to take it? I'm interested to see how you fare in the depths. You're guaranteed safe passage through the first floor."
"That's where the holding cells and... other facilities are. Once you get to the floor below, all bets are off. Try to return, and you'll be taken, and we'll go through the process of bringing you to us. Get caught while looking, and you can expect the same. There are people of ours down there. More will join them when they hear you are down there. There are other creatures down there that will strike to kill. Choose, Sora. Choose your fate."
"I'll take my chances before I side with the likes of you. Get out of my way, and I'll show you just how good I am."
"Show me then, Sora... show me what you're capable of. Who knows... maybe I'll be the one to bring you to your knees, and beg us for mercy."
He swiped at her again, quicker this time, shouting "I don't beg to anyone!" She didn't fade out quick enough, leaving a scar rapidly healing over her chest.
She looked down, watching it heal, then fade entirely. Only the cut in her clothes showed any evidence of what he'd done.
"Oh, you're good. I'll get you Sora. Get moving quicker so I can come after you already."
Sora pushed roughly past her, furious, and heading down the stairs. Her mocking laughter followed him down until she slammed the door on him.

The prison level had indeed turned out to contain rooms where people were tortured. He didn't want to think back to it. Guards and torturers alike watched him pass malevolently, as if daring him to assault them. Terrified inmates screamed at him for help. He wanted to, but he was determined to get out of this place, and no doubt if he tried anything here, they'd descend on him. There were loads of them up here. He was outnumbered.
Down here on the next floor though, things were different. It was a literal maze, every corner a potential threat. He'd met people dressed in all kinds of styles, always alone. Clearly this power of theirs wasn't as great for some as it was for others, because only some seemed to be able to fade out, and all that could, did it slower, leaving them vulnerable. There were other powers they showed too, speed, strength, throwing fire, or ice, or lightning, or other things. Some engaged him directly with a variety of weapons. So far, he'd made it through with no trouble - no doubt if more came though, it'd get harder.
By now, he couldn't find his way back even if he'd tried. He'd lost track of it in several of the fights.
Footsteps from up ahead. There were no junctions around in front or behind. Only a corner. He couldn't run before they turned the corner, so he turned it first, ready for battle. He was surprised by who he saw.
"Seifer? Is that you?"
"I'd hoped to find you, Sora. You're an interesting one. I thought you might take the offer to save your own life."
"Not a chance. What do you want, to see if I've changed my mind?"
"Why not? Reconsider, Sora. I can get you past what you've done, and get you a higher position than you'd have had if you'd just taken the original offer."
"What did they offer you, Seifer? What turned you over to them?"
"The same thing they offer everyone; power. It can do amazing things, with a little practice or patience. I can show you how-"
"Give it up. I'm not interested. I'm going to get out of here."
"No one even knows if she was telling the truth about there being an exit."
"I'll find one if there is."
"And if there isn't? There's no safe places down here. No places to get something to eat, unless you care to eat the monsters down here. I believe there's a few springs, though I've never gone looking personally. You also can't fight forever."
"I won't give up."
"Sora, tell me... what do you think will happen if you get caught?"
"Dragged back upstairs and put through the same as everyone else there, no doubt."
"Until you choose to join us, that is, but yes. Do you really want to go through that?" Sora didn't reply, so he continued. "Certain life and power unimaginable, or the possibility of death, starvation, and being tortured while looking for a potentially non-existent exit. I know what I'd choose. Take up my offer, Sora. End it before you have to go through that. Work for me."
"Get out of the way, Seifer, or I'll attack you too."
Seifer shook his head, but vanished, leaving behind an echo of, "You'll come to regret your choice later, Sora."