Hey guys! Welcome to a new crossover story that's been...literally four years in the making XD

I wanted to write a Fullmetal Alchemist/Rise of the Guardians crossover story for a long time (it's a favorite crossover of both myself and a close friend), and even started to do so back in 2017! In fact, you can still see the failed remnants of said story on Fullmetal Alchemist Amino to this day, which were ultimately heavily edited and repurposed into the first couple of chapters of the final version of this story, Frost and Fullmetal! I also have a FMA/ROTG oneshot already up on AO3, which I may post here as well once this story is done? We'll see!

And now, for the first time in my fic writing career, I actually waited until I fully wrote a story before I began to post it, so there'll be no missed updates this time around! Yay! It's eleven chapters long and a new chapter will be posted every Tuesday until it's done. Don't worry, though, all of the chapters are pretty long!

In any case, it's time to introduce you guys to my version of a crossover that I've wanted to share for a long time now. I hope you enjoy it as much as I do :)

~1~

The Stranger

Cerulean eyes glowed softly in the dim light as they surveyed the darkened streets of the unfamiliar city. The boy to whom the eyes belonged shifted his position slightly on the rooftop on which he perched, sliding down into a kneel while he watched the empty area beneath him.

"Strange…" he murmured, seemingly to no one. "I don't recognize this place at all…"

He received no reply besides the gentle night wind ruffling his snow-white hair in such a way that it could almost be described as fond. Apparently satisfied with the cool breeze's response, a smirk played at the boy's lips.

"Don't bother telling me off...I know I shouldn't have done it."

After a few more moments, the blue-eyed boy straightened once more, stretching his long legs and slinging what looked like a wooden shepherd's crook over his shoulder.

"Well, I might be hopelessly lost…" he commented, seeming rather unconcerned about such a fact. "But I just need to find the snow globe, and then I can get out of here."

The wind once again lightly swirled around the boy as though agreeing with him.

He gave a slight grin and nodded, his silvery hair catching the moonlight at just the right angle to wreath him in a mysterious, almost ethereal aura as he moved to the edge of the rooftop.

"Nothing more to do but start looking, huh, Wind?"

Without another word, he jumped.

()()()()

Edward sincerely wished his brother had at least some semblance of self control when it came to collecting stray cats off the street. Not only had he just come from delivering a report to a certain bastard colonel that evening, but now, he had just discovered the little tabby Alphonse had hidden within his armor. His day had been absolutely fantastic, and he meant that in the most sarcastic way possible.

"Damn it, Al!" Edward complained. "I told you, when you see a cat on the street...leave it!"

"But Brother…" Al said softly, holding the small cat as gingerly as his large hands would allow him to. "It looked so lost and lonely...it wouldn't have been right to leave it!"

"I don't care! It would have been fine on its own!"

"Brother…"

"Don't 'Brother' me! Put it back!" Edward rubbed his forehead in exasperation, seconds away from taking the cat and pitching it into the nearest alleyway himself.

He would have too, had it not been for the boy that fell out of the sky.

No...that was the wrong word. He didn't so much as fall...rather, he gracefully jumped off a tall building and landed perfectly on the ground a few feet away.

Which obviously shouldn't have been possible.

The strange boy didn't seem to notice the Elric brothers' blank stares, giving them a few more moments to take in his appearance, which was equally as strange as his landing. He held an odd-looking shepherd's crook in one hand, and both it and the dark blue sweatshirt he wore were dusted with what looked like frost. His skin was as pale as a corpse, his hair white as snow, and his electric blue eyes practically glowing as he looked around. By the way his gaze swept curiously over the streets, the boy seemed lost, though not entirely bothered by it, oddly enough.

"Um...Brother?" Al asked tentatively. "You...saw that too, right?"

"...yes, Al. Yes I did."

Suddenly, the boy began to speak. "This is weird…" he mumbled to himself, only just audibly enough for the brothers to hear. "Where the hell am I…? Everything looks so...dated. It's like...what, the early 1900s…?"

Edward blinked, raising his eyebrows. Unless he was, for some reason, sorely mistaken, it most certainly was the early 1900s, and had been so for over a decade at that point.

So how come this guy hadn't seemed to get the message?

The Fullmetal Alchemist scowled, trying to push back the sudden flare of curiosity that threatened to overtake him. Some weird guy jumping off buildings and mumbling to himself was far from his business. All he wanted to do was to finally get back to the military dorms he and Al were currently staying at and get to work on studying some of the alchemical library books they had picked up earlier in the day before visiting Edward's superior officer. Their research was infinitely more important than questioning a random stranger's odd activities.

...unless, of course, said odd activities were somehow connected to a certain Stone…

"Hey, Al," Edward whispered to his younger brother. "I say we talk to that guy. Jumping off a building and landing without a scratch…? Sounds like something we could look into."

Alphonse quickly nodded. "Okay!" he whispered back. "But please, Brother, try not to be too aggress - "

"HEY YOU!"

The younger Elric brother gave an exasperated sigh as the strange white-haired boy appeared to nearly have a heart attack in response to Edward's shout. With a startled yelp, the boy had leapt several feet back, just barely managing to avoid dropping the oddly curved stick he was holding, and was now breathing heavily, trying to regain his composure. His eyes widened as Edward began to walk purposefully up to him.

"Brother, I think you're scaring him!" Al scolded his brother, crossing his large metal arms.

"Then I guess he'll just have to deal with it," Edward said, brushing him off with a roll of his eyes. He pointed one gloved finger directly at the boy. "We need to talk to you!"

For what must have been a solid ten seconds, the stranger simply stared at them. Finally, he jumped a bit, did a quick double take, then coughed slightly and exclaimed, "Wha - me!?"

Ed promptly assumed a deadpan expression. "Who the hell else would I be talking to?"

"Um…" The boy hesitated, shifting his weight from side to side in an almost textbook display of nervousness. "Someone...else…?"

"You're the only one here besides us!"

The stranger quickly ran his fingers through his hair, frowning. "I-I know that! It's just that most people can't see…" His eyes widened slightly at his own words, and he immediately rushed to correct himself. "I-I mean...they can't stand me! They can't stand...to talk to me...y-yeah. That's it." As if to accentuate the pure anxiety and uncertainty that radiated from him, at the end of his sentence, he added a nervous chuckle paired with the most awkward grin Edward thought he had ever seen.

Ed and Al shared an unimpressed glance. It was clear that this boy had never learned how to hide obviously suspicious behavior.

"Well…" Edward said slowly, suppressing the urge to let the stranger know how much of a complete and utter dumbass he obviously was. "I think we can stand to talk to you for a while. We've got some questions to ask you!"

As he seemingly forced down the odd display of panicked bafflement, the strange boy's eyebrows raised, and Ed noted that his muscles visibly tensed as though he was expecting to be attacked. "A-As much as I'd love to answer, I've kinda gotta get home quickly. Things to do, people to let know I'm not dead...that kind of thing."

"They're going to have to wait!" Edward insisted. "Because…" He pulled out his silver pocket watch and held it up for the boy to see. "It's for official business! As a State Alchemist, I demand that you answer every question I ask you!"

Rather than the sudden fear or quick, frantic display of respect Edward had been expecting, the boy simply stared blankly at him. "As...what?" he asked, tilting his head slightly to the side.

There was a silence.

"You...don't know what a State Alchemist is?" Alphonse asked in surprise. Even those with no knowledge of politics or the science of alchemy at least knew who the State Alchemists were. The so-called "dogs of the military" were even infamous in the countries that neighbored Amestris, for...less than peaceful reasons.

So either the guy had come from somewhere much farther away, or he really was just a dumbass.

"Uh, no," the boy replied with little more than a blink. "Should I?"

The Elric brothers stared at him, and, under their fixed gazes, he appeared to become increasingly uncomfortable. He cleared his throat awkwardly. "So...I'll just be going, I guess."

With that, he turned on his heel - the guy wasn't even wearing shoes, Edward noticed - and began to walk away. Edward's eyes narrowed. "Oh, no you don't," he mumbled. "You're staying!"

He ran forward in an attempt to get in front of the boy and block his way. His intention was not to attack (yet), but the albino boy seemed to assume differently. His blue eyes narrowed and he broke into a run, his long legs easily outpacing Ed's...not quite as long, but definitely not short ones.

The blond alchemist narrowed his golden eyes in irritation. "Doing this the hard way? Fine!" While still running, he clapped his hands together and touched the ground. Blue sparks flew, and a towering wall suddenly sprung up out of the ground, right in the boy's path. It curled around to block him on both sides, making it impossible for him to run anywhere but directly at Edward.

His cerulean eyes widened, then narrowed, and, to Edward's surprise, the boy, undeterred, simply jumped onto the wall and rapidly began to scale it. Strangely enough, something seemed to be actively keeping him from falling, but from behind, the older Elric brother couldn't tell what it was. Either way, he was understandably more focused on being angry over the fact that the boy was climbing up a nearly flat, vertical surface like it was nothing. "HEY!" he yelled indignantly. "What the hell!?"

Without a word or even a glance back in Edward's direction, the boy reached the top of the wall and leapt to the other side. Ed let out a growl of frustration as he clapped again, this time taking down the wall. As he continued running, he called over his shoulder, "Help me out here, Al! And leave the cat!"

"You're so mean, Brother!" was Alphonse's reply, but by the sound of clanking armor catching up with him, Ed knew his younger brother had complied with his demand.

"Keep him running!" Edward called out to the suit of armor. "I'll cut around and get him!"

"Got it!"

As Al continued running straight, Edward darted into a narrow side alley and clapped his hands together a third time. Blue sparks flew and a pillar quickly rose out of the ground beneath his feet, lifting him up to the roof of one of the buildings. He jumped off and immediately began sprinting across the rooftops, using smaller alchemically formed pillars made from the roofing material to propel him from building to building. It was the momentum from these repeated transmutations that allowed him to soon pick up enough speed to overtake the white-haired teenager.

"I've got you now!" he cried with a grin as he clapped yet again, forming a sort of slide that sent him careening off the side of the last roof and landing directly in the albino boy's path. Taking advantage of the brief moment the boy was forced to take in order to skid to a halt, he quickly clapped and transmuted the ground under the strange boy, causing it to rise up and encase him from the mid-chest down, successfully pinning his arms to his sides and locking his body in place.

"Good job, Brother!" Al called as he caught up with the two.

Edward gave a smug smirk, casually strolling up to the captured boy. "So…" he drawled, leaning over and using part of the transmuted ground encasing the stranger as an armrest. "Looks like we've caught you. Care to come with us and answer a few questions?"

"This seems a bit excessive, don't you think?" was the teen's only deadpan response.

"Maybe, but I don't really give a damn," the blond retorted. "Now answer the question. Coming with us without a fight?"

The boy took a few moments to consider his admittedly limited options before finally letting out a heavy exhale. "Fine," he mumbled. "I'll answer questions. But keep in mind...if I have to, I know how to fight my way out."

"And so do we," Edward replied. "Al, hold him." He clapped and allowed the ground to return to normal while the younger Elric brother took the boy's arm.

"Sorry about this," Al apologized sheepishly. "My brother can be a little...aggressive."

"I can tell," the boy muttered with a roll of his eyes.

The State Alchemist simply rolled his own eyes in response and started walking, the other two following just behind.

"By the way…" he heard Al say. "My name's Alphonse Elric, and that's my older brother, Edward Elric. What's your name?"

"...it's Jack," said the boy, after a short pause. "Jack Frost."

()()()()

Throughout the rest of the walk back to the military dorms Edward and Alphonse were staying in for the night, Jack did not resist once. In fact, he barely paid the boys any mind at all, instead merely looking around, seemingly interested only in his surroundings. To Edward, he looked almost like a sightseeing tourist, despite the fact that this part of town held nothing special.

The dorms were quiet when they entered, as it was the middle of the week and the early morning hours were steadily approaching. Thus, they fortunately were able to get to their room without being confronted by anyone who might ask why the brothers were leading a complete stranger into a military area. As luck would have it, even the few soldiers that were awake to guard the building simply saw the two alchemists and waved them past, not noticing Al angling himself in just the right way so that Jack would be hidden from their lines of sight.

As with most things, Edward didn't want the military to even remotely get involved with what he was doing.

"You know," Jack whispered as they entered their room. "If you didn't want anyone to see me with you, wouldn't it have been smarter to do this outside somewhere?"

"Shut up," Edward hissed back. "My research journal's back here, and I'm not about to wander the streets for hours just to find a quiet place. Besides, this puts you in our territory, so you won't be able to pull anything funny."

The boy merely gave a shrug. "Fair enough."

Alphonse took the albino boy inside and pulled up a chair for him across from the bed, where he sat down. Edward took a moment to shut the door and grab his journal to take notes in before sitting beside his brother, studying Jack with narrowed eyes.

"Alright…" he began. "You've got a few things you need to explain."

"Ooh, am I being interrogated?" Jack asked with a chuckle. "I'm guessing you're the bad cop."

"Just shut up and listen!" Ed whispered angrily. "What was with that stunt you pulled where you jumped off the roof? You landed without even a scratch!"

Jack arched a dark eyebrow that heavily contrasted with his silvery hair. "You saw that?"

"Yes," Edward said, rolling his eyes impatiently. "Now get to the point and tell me how you did that!"

The boy paused for a few moments, thinking over his answer. Then, he leaned back with another shrug. "It's complicated," was his only reply, much to Edward's chagrin.

"I can handle complicated," he growled irritably. "So spill it!"

"Brother, be more gentle and maybe he'll be more willing to answer," Al sighed.

"I'm liking good cop's approach better," Jack agreed with an irritatingly amused smirk, nodding in Alphonse's direction.

The blond's left eye was twitching wildly, but, acknowledging that Al was right, he forced himself to calm down, clearing his throat. "Okay," he said through clenched teeth. "Please, explain what you mean by 'complicated'."

Jack's smirk only widened. "Now you're getting it," he said approvingly. Then he shrugged yet again, much to Edward's annoyance. "Although I'm not sure how much of an answer I have for you. I doubt you'd believe me if I told you."

The Elric brothers shared a glance. The two of them were usually the ones on the delivering end of the "unbelievable" stories. Edward highly doubted anything the boy had to say would be any more ridiculous than the two of them could handle.

"Try us," the Fullmetal Alchemist challenged him with a grin of his own.

Jack arched an eyebrow. "So, you think you can handle it…" he mused. He considered Ed's words for a bit, then proceeded to shrug and smirk - both habits that Edward was gradually becoming more and more annoyed with. "Do you believe in magic?"

...

...what?

Just...what?

Of all the stupid things Edward had expected to come out of the definite-dumbass's mouth, magic had to have been the last on the list.

No, scratch that, it hadn't even been on the list.

Edward opened his mouth irritably to speak, but his younger brother beat him to it.

"Um...magic…?" Al slowly questioned as though uncertain of whether or not he had heard the boy correctly.

As if he hadn't just tried to turn the very rules of rational science upside down, Jack gave a casual nod. "Yep. Magic. Told you you wouldn't believe me."

"Well of course not!" Edward exclaimed irritably. "Magic doesn't exist!"

"Awfully close-minded," Jack commented. "You're not even going to hear me out all the way?"

"No!"

Jack shook his head. "Rude. Also, I thought we were supposed to be keeping quiet."

Edward scowled. "I need you to take this seriously! It's important!"

The albino boy merely chuckled. "I am taking it seriously," he said. "And I can prove it."

"Oh yeah?" Edward challenged, crossing his arms.

"How?" Alphonse added curiously.

For a moment, Jack was silent. Then, a slight smirk formed on his face and he raised his hand. Edward's skeptical expression dropped in an instant as silver wisps of frost flowed from the boy's fingertips, weaving together to form multiple tiny snowflakes in the air.

Ed's jaw nearly hit the floor.

"W-What the hell!?" the blond alchemist shouted in shock once he had found his voice, leaping up, his journal and pen tumbling to the ground. "That...that's not Equivalent Exchange! You didn't draw a circle, or even clap, or...what the hell!?"

"Okay, so...I have no idea what you're talking about," Jack drawled, letting the snowflakes slowly dance around his fingers. "But I told you. It's magic. No fancy stuff or whatever, you just...do it."

"B-Brother…" Al began hesitantly. "Maybe...maybe he's telling the...truth…?"

Edward idly wondered if dumbassery was somehow contagious.

Outwardly, he merely gaped at his younger brother, who quickly rushed to explain. "I mean, he created something out of nothing without even moving! And there were no transmutation sparks like a Stone would give off! What...what else could it be…?"

"It has to be something!" Edward growled. He grabbed the front of Jack's hoodie and pulled him up out of the chair he sat in, almost thrown off-balance due to the boy's weight being only a fraction of what he had been prepared to lift. Edward quickly righted himself, however, and proceeded to shout, "So what is it!? Do you have a complete Stone!? Something like it!? Who are you!?"

"Brother, you're going to wake everyone up!"

Ed attempted to offer a harsh retort to Al's words, but, suddenly feeling a cold sensation cross his mouth, found that he couldn't even move his lips. His eyes widened.

Was...was his mouth frozen shut!?

Jack seemed unamused but not particularly malicious as he effortlessly yet carefully pushed Edward away from him. "Listen, kid," he began, eyes narrowed into cobalt slits. "I'm not really in the mood for being screamed at. I don't know where I am, I've got to go find my way home, and I still have no idea why you two can see…" He paused, then shook his head. "...this just hasn't been my day, okay? So if you're done yelling and grabbing me, I'll answer a few more calm questions if you need it, and then I'll be on my way. Got it?" As he spoke, he shifted slightly so that the moonlight seeping in through the window reflected off of his skin and hair, forming a silvery, ethereal aura about him. To anyone else, his spectral appearance would have been intimidating.

Edward Elric, however, was not easily awestruck, especially when pissed off. Though he wasn't entirely sure why he bothered, he made another attempt to yell at the albino teenager. Unfortunately, all he could manage was a humiliating, muted, "MMPH!"

"Hm…" the boy mused. "I'll take that as a no, unfortunately." He stepped away from the furious alchemist. "Then I guess I'll be leav - "

"Wait!" Alphonse suddenly interrupted. "Please...we still want to talk to you, even if my brother's not the best at...normal conversation. I promise, though, I can ask questions calmly..."

Jack ignored Edward's continued attempts to scream at him and instead studied the suit of armor for a moment, a mildly skeptical expression on his pale face. Finally, however, he sighed and sat back down. "Fine...but please, make it quick. I really have to get home…"

Al nodded, relieved. "I understand. Now...do you know what a Philosopher's Stone is?"

The boy arched a dark eyebrow. "You mean like in Harry Potter?"

Neither Ed nor Al were sure how to respond to that (not that Edward could).

"Harry...what?" the younger Elric questioned.

Jack shook his head dismissively. "Never mind. Book series. Not important. Hm...I'm sure I've heard the term outside of that but I never knew exactly what it was supposed to be...isn't it like some magic stone thingy or whatever?"

"Thingy!?" Edward tried to exclaim, but it came out sounding more like, "MMPPHHYY!?"

"It's...not a magic thingy," his brother explained far more calmly. "It's an alchemical tool with the power to amplify ability to the point of completely bypassing the Law of Equivalent Exchange."

Jack stared blankly at him. "...you lost me at 'it's'."

Edward rolled his eyes in contempt, but the ever-patient Alphonse simply thought for a moment. "Well…" he began. "We practice the science of alchemy, which is dictated by the Law of Equivalent Exchange. Equivalent Exchange means that one can gain nothing without giving something of equal value. Alchemists like us have to follow that law, otherwise nothing we do would work. Like when we were chasing you and Brother made that wall in front of you; he used the materials in the ground to build something up above it. There always has to be equivalence. With a Philosopher's Stone, though, an alchemist could just...make something out of nothing."

"...so like magic," Jack said, one eyebrow raised.

"...kinda," Al relented.

Jack shrugged and leaned back. "Well, sorry to disappoint, but I don't have anything like that. And that's the truth, so...that's that, I guess. Any more questions?"

"Well - "

Suddenly, the door to the room swung open, revealing a very irritated dark-haired man in a royal blue military uniform. At his side was a similarly clad blonde woman with a carefully neutral expression on her face.

While Jack only stared in confusion, Edward's golden eyes narrowed at the familiar sight. "Colonel Bastard…" he growled. At least, that was what he attempted to say, but all that was audible was something like, "Murfel Mafnerd…"

"Fullmetal," Colonel Roy Mustang began in an exasperated, dangerously low voice. "Allow me to tell you a bit of a story. As I was finishing up the last of my paperwork, just pages away from being able to finally go home and sleep...I suddenly began to receive quite a few strange calls regarding suspicion of a stranger being brought by one of my subordinates into the military dormitories, as well as numerous noise complaints. Thus, instead of going home to my bed, I am here, talking to you. Now, as you can imagine...I'm not happy. So let me just say one thing...there had better be an excellent explanation for this."