Riku stood in front of the door to his childhood home, knuckles not quite touching the surface. His brain spun with a million reasons this was a bad idea as he tried to work up the courage to knock. What if they didn't recognize him? What if they'd mourned and moved on to another house or town? What if they were among the casualties from his foolish decision, part of the long list of people who failed to return even after the Islands' restoration? What if—

A gasp broke him out of his thoughts and he whirled around, looking into the eyes of his mother. Her shopping bag thumped as it struck the ground, milk splashing across the sidewalk. She whispered through her fingers, "Riku?"

"Hi Mom." He whispered, then looked away, unable to bear her shattered expression and tear-filled eyes. A moment later he was enveloped in a hug tight enough to crack his ribs, and his mother pulled his hands from his pockets to check him over for missing limbs and fingers.

"Look at you! My baby boy." She sobbed as she led him inside, chattering about how he'd grown and how she needed to call his father right now. Riku took a moment to just breathe in the familiar smell of home, which hadn't changed one bit in the years he'd been gone. Such a strange feeling. Was this nostalgia, or something more complex? He smiled as his mother wound the phone cord around her wrist and hands like she always had, waiting for his father to pick up.

"Yes, I know you're very busy but you need to come home right now. No, I can't explain why on the phone, just please. I wouldn't ask if it weren't important."

They waited in a somewhat tense silence. Riku's mother practically vibrated with all the questions she wasn't asking, and finally she jumped up to make hot cocoa. "Don't you even think about moving, young man." She said, and kept sticking her head out of their galley kitchen to check on him. He smiled each time, but felt the shame and guilt build up a little more each time she did it. He was sipping his watery hot cocoa when the front door opened.

"Honey? I'm home, why are the groceries on the"—

Riku stood up and faced his father, squaring his shoulders and placing his cocoa down on the end table. "Hello, Dad," he said, smiling as best as he could through the hot tears suddenly stinging his eyes.

His father just stared for a long moment, then started to laugh. He laughed and laughed till he could hardly breathe, and Riku was honestly getting a bit concerned for him. When he finally composed himself, he sniffed loudly and said, "You are so grounded, mister."

Riku chuckled. "I missed you, too." Then he was being hugged by both of his parents, and it was the most wonderful warmth he never realized he'd longed for.

Explaining his absence was more difficult than he'd expected, mostly because of the fact that Destiny Islands, in his parents' memories, had never been devoured by darkness. Luckily, summoning the Keyblade and casting a few spells did a lot to defend his case. Riku let them each hold it for a moment and explained that it was not only a master key, but also a sword, a magic wand, a ward against darkness, a summoning stile, and a way to see into people's hearts and share their memories. Until he listed out all the things it could do, he hadn't realized just how versatile it was.

The trouble started when his mother broached the subject of Riku returning to an ordinary life. "Of course you'll need to enroll in high school, even though the year's half started."

Riku rubbed the back of his head, knowing this would be awkward. "Actually, I have duties as one of the last remaining Keyblade masters. I don't think I'll be able to go to school with any regularity." Even without the threat of Xehanort still looming over their heads, they still needed to locate Master Aqua and get her to rescue Ventus. If Terra's heart was still recoverable, he needed to be brought back too. Compared to a mission of that scope, Language Arts just seemed superfluous.

"You are going to school. Non-negotiable." Riku sighed, having anticipated this. When he looked to his father, he found no camaraderie there.

"Your mother is right. You need your education. And grounded kids don't get to go on adventures with magic swords."

No one had called Riku a kid in ages, so he had to laugh. "Okay, okay, I'll go." He could always just take the tests and use some medical excuse to get out of class when necessary.

The truth was, he could probably sit and pass his exams right now. Maleficent hadn't cared for Riku's education in any subject other than the use of darkness, but she mostly left him to his own devices. During those long hours he'd spent alone in Hollow Bastion, he could usually be found in the library. He picked up whatever book caught his eye and read it all the way through, sometimes getting through four or five books in a week. Some of them had been older than his grandparents, handwritten by scribes and doodled in by generations of bored students. Others were newer, but none seemed to be from the current century.

This habit left Riku with a peculiar knowledge base, ranging from biographical knowledge of members from the original Parliament of Radiant Garden to proper methods of child-rearing as practiced by Moogles. Books about divination, the study of light, the history of blood use in rituals... nothing was off-limits, and there was no curriculum. He had gaps in his schooling larger than the space between worlds, but he was never bored.

Then DiZ found him in the Realm of Darkness, and moving into the mansion changed his experience quite a bit. DiZ maintained his library personally and regularly added to it, making his collection much more up-to-date than Maleficent's. At first he was astonished that Riku enjoyed reading, but within a month, he developed a progressive reading list for his new pupil. Every week, he set aside a few hours to meet with Riku for what he called 'check-ins.' He had to be quick on his feet during these open-ended sessions, where DiZ would fire off author names or chapter headings and expect Riku to analyze the content and explain what he'd learned. Riku found himself studying advanced mathematics, the scientific method, physics, philosophy, and literature. History was rarely discussed, and when he asked about it, DiZ just shook his head slowly and said nothing. Two weeks later, over yet another tasteless meal of over-boiled vegetables, DiZ stated, "History is only worth studying through the use of primary documents, and those documents I would have you study are not accessible to me. I trust you understand."

Riku agreed, and did not bring it up again.

All of this meant that high school would be an exquisite torture for Riku, as he had grown used to one-on-one instruction and challenging subject material. He still had it better than Sora, who'd been asleep for over a year and whose memories of school were fuzzy at best. Namine had been too busy ensuring all of the most vital pieces were back to care about whether or not Sora remembered quadratic equations, and he hadn't been the best student even before the memory fiasco. Riku tutored Sora in every subject except Physical Education, which was a complete joke for someone who had Flowmotion at his disposal; despite his best efforts, Sora scraped by the first semester with barely-passing marks. His mother wasn't happy, but heard from Riku just how badly Sora's mind had been damaged and concluded that her son was now mentally disabled. Riku didn't tell Sora that, and didn't try to discourage her once she made it clear that was the only reason he wasn't grounded too.

He didn't have to wait long for his first summons.

"Master Riku, I have a matter of grave importance to discuss with you. Please meet me at the tower."

"But I wanna come with you and see Kairi and Lea," Sora whined, but Riku just said dryly,

"Try not to get into too much trouble." The Gummi ship the King had lent them was smaller than the one Sora and friends usually used, so he couldn't come along even if he'd finished all his homework.

So Riku left him behind, the rush of flying through the Lanes Between with nothing but rubber between himself and the vacuum of space making his heart race with excitement. He'd never liked traveling through the corridors of darkness.

When he arrived at Yen Sid's tower, Kairi and Lea were sparring on the front lawn. Riku dropped to the ground some distance away so he could observe. Lea really was getting better, though he still tried to throw his Keyblade more often than most, and Kairi…

Kairi was radiant.

The light shone out of her heart in the way it only ever did for Princesses of Light, and her Keyblade flashed through the air with precise motions. It was clear that she was a new student to the art of combat, since she had yet to develop her own fighting style, but Riku could tell she'd taken to her lessons with unusual ferocity. Something about 'I'm not being left behind ever again by you two idiots!'

Yeah, Riku's ears were still ringing from that lecture. Though he'd be the first to admit that they deserved it.

Lea saw him first and dropped his guard to wave. Kairi took advantage and had him on the ground before Riku could blink. "Gotcha!" She shouted, Keyblade at Lea's throat.

"Okay, okay, I forfeit. Yeesh. Let me up. Hiya Riku."

"Riku?" Kairi spun around and saw him. "Hi! Were you watching?" Riku grinned at Lea.

"I was. You're getting pretty dangerous."

She stuck out her tongue. "Just try and leave me behind next time."

"Wouldn't dream of it. Is Master Yen Sid home?"

"Yeah, course. Cid's here too. Said he's got something for you." Lea said, picking himself up from the ground and banishing his Keyblade. "I think I'm about done for the day, Kai…" He groaned melodramatically and put a hand on his back. "You've gotta take it easy on your elders."

"What, giving up already?" Kairi asked, raising her eyebrows. Riku smiled at the familiar words. Kairi giggled and stuck out her tongue. "Pathetic."

"What d'ya mean 'already'? We've been out here since dawn!"

Kairi banished her Keyblade and put her hands on her hips, leaning forward with a stern expression. "You're just lazy, admit it."

Riku left them to it, laughing under his breath. At first, Kairi had been understandably suspicious of the person who'd kidnapped her, but it seemed like the ice between them had finally thawed a little. He took the stairs three at a time and pretty soon was at the top of the tower. Right before he could knock, Yen Sid's voice came in through the door. "Come in, Master Riku."

"Master Yen Sid." Riku said, walking in and standing at attention. "You asked to see me?"

"Yes. In fact, it is Cid who needs you first."

Riku turned to Cid and grinned at the pile of metal plates clutched in the old engineer's hands. "Is that it?" He asked, leaning forward to get a better look.

"Yup. Take a gander. We're mighty proud of this."

He took the plates and snapped them on, feeling them heat up and hum as they adjusted to his arm. The plates covered Riku's left bicep, and a single guard with a hinge hung over his elbow. He twisted his arm around, but the armor didn't obstruct his range of movement at all. It was surprisingly light, not cheaply made but supple and fitted. A round gem was nestled in between the top plates. "Alright, Cid, how does it work?"

"You jest press the little round plate there and it'll jump right on you." Riku noticed Cid edge away from him and braced himself, then used two fingers to depress the plate. There was a flash of white light, and before he could even feel it happen, he was covered from head to toe in deep purple plates of armor. He raised both arms, astonished by how quickly that had happened. Cid let out a noisy, relieved breath.

When Riku turned his head towards Cid, he chuckled. "Oh, nothing," he said in response to the silent question, "I'm jest glad it didn't blow up this time. Don't worry," he added, probably trying to reassure, "it hasn't since the very earliest prototypes. I jest wasn't sure how it'd react to someone who hadn't worn it before."

"How do I put it back how it was?" Riku asked, voice muffled through the full helmet.

"You jest yank the little latch under the plate where the button was. We didn't want it to be too easy to get to, so we moved it from where it used to be. The old design made it too easy for an enemy to disable the armor while fighting, and that was no good."

Riku shivered at the thought of what would happen to him should an enemy in the Lanes Between succeed at disabling his armor while he was flying through space junk. If an asteroid didn't kill him, he'd suffocate in the vacuum. "Good idea." His fingers sought out the tiny switch and he pulled it, causing another flash of light and collapsing the armor back to its portable form.

Cid pointed at it. "Now that you got that thing on, you can try throwin' your Keyblade up and commanding it to 'Glide!' It should transform into your own personal ship. Just don't do that in here, since I'm bettin' Mr. Yen Sid likes his ceiling where it's at."

"Yes, thank you, I rather do." Yen Sid said dryly, glancing up. "Let us take this outside."

Once Riku figured out the glider and they returned to the tower, Yen Sid stroked his beard thoughtfully. "I am afraid that there is a new threat to the worlds. Or rather, a very old one. I had thought this universe was rid of it for good, but now my reports tell me of hideous black creatures made of shadow and sand, like Pureblood Heartless but more versatile in form." His fingers swirled over the surface of the desk and conjured an image of a black horse, rearing its head and hooves fiercely. Its eyes were the blank yellow of the Pureblood Heartless, but deeper in shade. As Riku watched, the horse melted into a puddle of shadow and reformed as a soldier in full battle gear, brandishing a sword.

"The source of this darkness is unknown to me, but it appears to be linked to that of Nightmares. In other words, these are Nightmares of a different form—one based in people's fears, rather than their darker impulses—and the plague has begun to spread. Your task is less simple than it sounds: track down the leader of these Nightmares, and figure out if we need to assemble who we can to fight."

"They have a leader? Like Xehanort?"

Yen Sid shook his head, slowly. "Xehanort has never led the darkness, only used it. Heartless can be summoned, but not controlled. Even Nobodies are ruled only by impulse, though they accepted simple commands from the Organization. No, this form of darkness is more capable of strategy than any you have seen before. They can plan ahead, work in groups, and adjust to changing situations. And they are very intelligent. Be wary of traps they may set. My research thus far indicates that they play a long game."

"I'll keep that in mind."

"Good. As far as we have been able to track it, these creatures originated in a world you have never been to before. It exists on the edge of the known universe, and will take some time to travel to." Yen Sid curled his fingers over the desk and pulled up the image of a blue-and-green planet. "It's considerably larger than most worlds around here, I would say easily twenty times the size of the largest world you've been to thus far. There are over six billion people living on it."

Riku's mouth dropped open. "Six billion? Sir, are you sure?"

"I believe the number is actually closer to seven billion. You will need to rely on luck and skill to find what you are looking for. I cannot offer much assistance here. The world is too far for me to scry with any degree of accuracy. Let the light be your guide."

There was nothing else to say. Riku bowed and left to prepare for a long journey.

For some reason, diving into a world seemed to put Riku in the right place at the right time. Maybe the power of Light affected his travels, or maybe he was just lucky. When that thought crossed his mind, he laughed. As if he'd ever had a shred of luck. More likely the universe was just arranging things to its own liking and he was along for the ride.

Despite this, he questioned the universe's wisdom when it deposited him at the edge of a snow-filled clearing full of children shrieking and flinging snowballs at each other. Out of old habit, he stepped back into the shadows cast by a nearby tree. His yellow and white vest wouldn't do as much as his old cloak to help him blend in, but hopefully it would give him enough time to assess the situation.

There were about ten children, all the same age, shouting and making a good effort at murdering each other with snowballs. Riku shivered just watching them. They seemed to be having fun, but he'd grown up on a tropical island and couldn't see the appeal.

Almost immediately, Riku noticed that more snowballs were being thrown than were being made by the children. Riku scanned the perimeter of the clearing for the source, and pretty soon a boy sitting on a tree branch far above the ground caught his eye. He looked older than the children playing, but no older than Riku, and held a twisted shepherd's crook across his lap. His free hand danced over the air like a pianist's, and Riku realized that he was actually making it snow. With a twist of his fingers, he conjured another pile of snowballs and began to almost casually toss them into the fray.

"Hey! You're cheating!" One of the girls yelled, drawing Riku's attention. The boy she was pointing at stuck out his tongue.

"Am not!"

"Are too!"

Riku looked back at the boy on the branch in time to see him breathe into one of his snowballs and throw it at the girl. When it struck true, her anger cleared and she started to laugh. "It's okay, we'll still beat you!" She vowed, scooping up a whole armful of snow and retreating behind her side's measly fortress. Riku had to smile. She reminded him of Kairi.

The teenager watched the children with a sad smile on his face. None of them seemed to notice him or his magic, and just a few moments later, a sharp whistle pierced the trees and all the children jumped. "That's my mom," The boy who had been accused of cheating said, pouting and brushing snow off his jacket. "I gotta go." After that, the fight was declared a draw, and all the children started filtering home. When they'd gone, the teenager leapt from his branch and floated gently to the ground, bare toes and staff digging into the snow. "That was a fun snow day, brought to you live by Jack Frost! Same time tomorrow?" He called after them, clearly not expecting a response. Riku stepped out from his hiding spot and cleared his throat, deliberately not making eye contact so that he wouldn't seem threatening.

Jack spun around, holding his staff out and narrowing his eyes. "Where'd you come from... oh, don't tell me, you're some kinda freak or something, now I gotta stop those kids from coming back here tomorrow, great, thanks."

Riku raised his eyebrows. "I'm not a freak."

Jack dropped his staff. His eyes were wide as he knelt down to pick it up, and he stared at Riku like he'd grown an extra head. "You can see me?" He asked, mouth open.

"Yes, I see you."

"B-But you're an adult. A human adult, if I'm not wrong."

"You're not wrong." Riku glanced down at Jack's bare toes, which he was curling into the snow absentmindedly. Jack Frost, huh? If the name was accurate, he probably didn't need shoes. "I'm guessing most adults don't see you."

"Most people, even kids, don't see me. I'm used to it." Jack shrugged. "Does that mean you believe in me? Were you part of the fight against the Nightmare King? You're about the right age, but I don't remember you—"

Riku shook his head against the barrage of questions. "Who's the Nightmare King?"

"That's a no, then." Jack went back to looking at Riku like he was an unexpected growth in a petri dish. "Why were you watching those kids? That's a little creepy, you know."

Riku didn't know what to say to that. He wasn't supposed to let on that he was from another world, but he thought Jack could probably tell from his odd choice of clothing for this climate. "I can be a little creepy." He admitted, shrugging. "I'm not used to people seeing me, either." That much was true. He'd spent almost two years hiding from everyone, including himself, and being possessed by darkness hadn't given him much time for a social life.

Surprisingly, that seemed to work. Jack relaxed, and began to twirl his staff with one hand. "So what brings you to northern Russia in no sleeves? How'd you even make it this far with that getup?"

Riku breathed out a small Dark Fira spell to warm his bones and smiled grimly at Jack's shocked expression. "I'm not exactly a normal human." He said dryly, as the purple flame dispersed.

"No kidding. Did the Man in the Moon give you power?" Jack asked, reaching out like he wanted to try and feel the heat left over by the flame.

Riku shook his head. "I don't know any man in the moon. Mine is a different kind of power." He debated for a moment, but the Keyblade had probably led him to Jack for a reason, so he reached out to his side and pulled Way to the Dawn from the ether. Jack jumped back with surprise when it materialized, bringing his staff up in a defensive pose.

"How did you do that?"

"It's always with me, but I don't like to come to a new place with a weapon drawn. Tends to give the locals the wrong idea." Jack lowered his staff slowly, stepping forward again once it became clear that Riku wasn't going to attack him.

"Hah, you're telling me. So what is that thing? I've never seen a weapon like that."

"It's called a 'Keyblade.' It gives me my power."

"Huh, go figure." Jack squinted at it. "No offense, but it looks a little silly. You really fight with that?"

Riku gestured towards Jack's staff, raising one eyebrow. "You really fight with that?"

"Point taken." Jack grinned. "You still haven't answered my first question."

Riku thought back and shook his head. "Sorry. I'm looking for something. Maybe you know of it. It's called 'living darkness,' and takes a couple of forms—"

"—Nightmares and Fearlings." Jack sat down in the snow, like he'd suddenly forgotten how to stand. "Yeah, I've heard of them. You said you didn't know who the Nightmare King was, though."

"I don't. Really, I don't know much of anything about it, except that it's smarter than normal Heartless and Nobodies, and it's, er, spreading. I'm supposed to find out how and stop it."

"You're a little late to the party there." Jack shook his head once, pushing his feet through the top crust of snow. "We defeated Pitch almost a decade ago."

"Pitch?" Riku sat down in the snow next to Jack. Not like it would make him any colder.

"One of his names, Pitch Black. He's also the Boogeyman and the Nightmare King. And about a decade ago, he launched an assault on the entire planet. I'm guessing you must be an alien or something, or you'd remember it. All the hope and light in the world started going out, and we almost lost. It was close," he clutched his staff to his chest with both hands and gulped, "Too close, really. But we won, and he's been imprisoned ever since."

"The darkness tried to devour this world?"

"Yeah." The wind had picked up with Jack's worries, and Riku wondered how much power he must have, to so thoughtlessly command it. He couldn't stop himself from shivering as it stole his body heat. Jack noticed and clenched his fist, stopping the wind. "Sorry."

"Thanks." Riku cast another fire spell, melting some of the snow around him. "So I think I heard you say 'we.' Who else fought the darkness?"

Jack puffed his chest out, grinning. "The Guardians! The five of us were given power by the Man in the Moon and we protect the world's children."

"Guardians, huh?" Riku considered that for a moment, wondering if any of them had the potential. He'd have to meet them all and find out.

"Yeah, like I said, we defeated Pitch and he's been in his lair ever since. North put a spell on the entrance so he'd know if Pitch left, but he hasn't yet." Jack glanced up at the sky, already darkening as the sun set. "He calls us with the lights, when he needs us to assemble."

"If he's your leader, I should go talk with him."

Jack stared for a moment, then started to laugh. "Did you seriously just say 'take me to your leader?'" When Riku tilted his head, puzzled, Jack laughed again. "No, it's okay, sorry, just. Movies. Anyway." He leapt up and diamond dust flew in every direction, making Riku hold his arm up to shield his face. "Sure, I'll take you to see North. Christmas is over now, so he won't be too busy." He offered a hand to Riku, who took it and pulled himself up. Even with the Fire spells, his skin was getting numb. "Um, you can't fly, can you...?" Jack asked, squinting at Riku like he was waiting for invisible wings to appear. Riku shook his head. The Keyblade glider worked between worlds, but it was too conspicuous to use on-world. "It's across an ocean, is the problem, and I don't have a boat."

"We can use my portals." Riku swirled his hand through the air and pulled up a dark corridor. After returning to the Islands, he'd unlocked the ability with a lot of practice and not a little bit of guesswork. He couldn't yet travel between distant worlds with the corridors, but they were okay for short trips. Jack gaped at it, reaching out with his staff to poke the writhing purple clouds within.

"Huh, those are like North's. Only more... shadow-y. You're not gonna shove me in a sack, are you?" When Riku tilted his head, betting that was an interesting story, Jack just grinned with one side of his mouth and shrugged. "Lead the way, then."

So Riku did.

Hello, I'm back with a crossover no one asked for. Hoping if I post it here it'll get me back to the rewrite it so desperately needs. This is going to be a fairly long story with some slow-burn romance (unrequited Soriku leading to eventual SoRiKai, and eventual Pitch Black/Jack Frost) but it's mostly adventuring and will remain a hard T since I'm not much of a romantic at heart. Full tags/warnings/et cetera will be posted on AO3 and updated as I decide what I'm doing. Leave a review if you can. Thanks!