A/N: This is a Darker than Black and Fullmetal Alchemist crossover, but you do NOT have to have watched Darker than Black to understand it. Everything is written in terms of the Fullmetal Alchemist manga/Brotherhood.

This fanfiction starts right before when Barry the Chopper attacked Lieutenant Hawkeye in the manga, which I believe is around Chapter 31 of the manga and around episode 16 of Brotherhood. However, there are spoilers beyond that point in Brotherhood/the manga, so beware if you've just started the series.

I do not own Darker than Black or Fullmetal Alchemist

Read and review! :)

Central City had always had its fair share of trouble. Terrorist attacks and assassinations were among the many crimes that were far too often committed in the capital of Amestris. So when the wail of the Military Police siren echoed out of a police car speeding down the road, Central City's citizens just made sure to get out of the way and didn't think about the incident any further. After all in a city so big, what was the likelihood that someone they cared about was in trouble?

However, a man in his early twenties who appeared to be a Xingese foreigner, and who had been shopping at a nearby store for groceries did not seem to share this view. He glanced after the car as it raced down the street with the peculiar blank expression, thinly veiling some kind of emotion. When the man saw it turn at the next corner his impassive mask slipped a bit more to reveal a hint of anxiety on his face. He thanked the store vendor and walked briskly with his purchases towards the corner where the car had turned. As soon as he rounded the corner, he put down the food and started running, making people shout in annoyance as he roughly pushed past them. He turned another corner, and his eyes widened as he saw the MPs already getting out of the car and swarming the building that had been his destination. His gaze swept calculatingly over the gathering of police, and, seeming to reach a decision, walked up to the nearest police officer, a grumpy-looking, overweight old man who seemed to be giving orders to the gaggle of police.

"Um… Hello. Can you tell me what's going on here?" the man asked somewhat sheepishly as he rubbed the back of his head. His manner had changed as soon as he had approached the officer—he now had a goofy grin on his face, and all seriousness was completely gone from his expression.

"…Do you live here?" the policeman asked suspiciously.

"Yeah, I just moved into one of the apartments a week or so ago. I thought I was choosing the safe part of town, but I guess not," he laughed, gesturing at the police who were still gathered outside, and appeared to be radioing in for back-up. They still hadn't attempted to invade the building.

"You're not from here are you?" the policeman replied, ignoring the man's previous comments, and still clearly cautious. "Do you have your documentation with you?"

The man looked a little taken aback, but smiled nonetheless. "Of course." He dug a couple of papers out of his coat pocket and handed it to the police officer.

The police officer examined the papers carefully and grunted in dissatisfaction when he found nothing wrong. He kept holding the immigration papers anyway. "Looks good," he growled. "But for all I know you might just have a really good forgery."

"Uh…" the Xingese man replied, nonplussed.

"Huang, are you bothering another innocent bystander again?" Another policeman had noticed the pair's exchange and was now standing behind Huang. The newcomer shot Huang a look of exasperation.

"In work like this, suspicion is the only thing that has kept me alive over all these years," growled Huang. "You better remember that if you want to live, Isozaki. You're still just a rookie at this. This guy just moved in about the time the murders started, and he's a foreigner. He could have easily faked his immigration papers."

"Why are you suspicious of foreigners? Aren't you from Xing yourself?"

"Exactly. So I know for a fact that the best assassins in the world come from Xing. There are plenty of experts because of all the assassination attempts on the fifty royal families."

The Xingese man looked at him in shock. "Wait—you think that I'm an assassin?!"

Huang didn't even look at him as he continued. "And all the best killers are monsters that look and act like normal humans."

The other policeman covered his face in embarrassment. "I'm really sorry about this," he apologized to the Xingese immigrant, who was still staring at Huang in disbelief. It was perfectly understandable that Isozaki didn't seem to find the man suspicious—he appeared to be quite normal, if not very rich. He was wearing faded jeans, a clean, but clearly old, long white shirt, and a slightly ragged green jacket. "There have been a string of murders of important people around town lately, so I guess everyone's really on edge."

"It's okay, I guess…" the Xingese man replied uneasily. "But can you at least search my apartment before you take me in for questioning? I've got a night job in a couple hours, and as you can see," he said, gesturing to his worn-out clothes, "I really need the job."

Huang glared at him, but consented. "Alright. Li Shengshun… is it?" he asked with a glance at the immigration papers as if he doubted the name's authenticity. "We'll keep you in custody until the building search is over. If we find even one thing suspicious," he added with a scowl at Li, "we're taking you in. Got it?"

Li nodded, albeit somewhat reluctantly. "Sounds fair. But why aren't you guys going in already? I would still like to get to my job, if at all possible."

"Well, we told you that this assassin killed several important people in Central City right?" said the younger police officer. "We're waiting for back-up from a state alchemist. We're just here to stop them if they run for it."

"This guy must be really dangerous…" Li mused. "I heard state alchemists are the best at taking down criminals like this. But…" Li tilted his head curiously. "Why did you say 'them'? I thought you were just after one assassin?"

"Never you mind," interrupted Huang gruffly. "If you're not him, it doesn't concern you."

"Huang, it can't hurt to tell him," Isozaki interjected with a hint of aspiration in his voice. He turned back to Li and whispered, "We've been hearing reports that he has this silver-haired girl that spies for him. We need to catch her too, because according to our sources," he lowered his voice and leaned towards Hei. "He'll do whatever we want if that girl is in trouble. Did you ever see any silver-haired girls around the apartment building?"

Li nodded thoughtfully with the pleasant expression still on his face, but his eyes seemed to harden at the statement. "Oh… so you're capturing the girl traveling with the assassin… so you can torture her to get the killer to talk."

The younger policeman looked a bit surprised at Li's choice of words. "I guess that's one way to put—" his voice was abruptly cut off as he gasped in pain. He looked down to see a knife handle sticking out of his stomach. He looked up farther to see that Li had pulled out a knife out from under his jacket and stabbed him. Isozaki collapsed on the ground, blood dribbling out of his mouth, eye's wide.

"And you call me a monster?" asked Li with contempt thick in his voice. His eyes were enraged, and his face had changed back to the cold mask he had worn before approaching the police. He had found out what he had wanted to know, and all pretenses of being normal were immediately dropped.

"Isozaki!" yelled Huang, not even seeing Li as he ran over to the young police officer.

Li could see the heads of all the police officers turn as they heard the shout. "Tch!"

Some of the officers raised their guns, but one of them threw out his hand to hold them back and shouted, "Don't shoot! You'll hit Huang and Isozaki!" As the policemen hesitated, Li in one fluid motion threw a wire snap-hook that was attached onto a belt hidden under his long shirt. The hook wrapped around a balcony on the fourth floor, and he immediately retracted the wire, which launched him up to the balcony underneath it on the third floor. The policemen watched him, open-mouthed.

"Don't just stand there, open fire!" shouted one.

"We can't!" yelled another. "We haven't evacuated the building yet!"

"Surround the building!" Huang ordered from his place at Isozaki's side in a firm voice. "Cover all exits, and make sure you watch the windows. Don't let him get away!"

The police officers all ran off in different directions as they raced to cover the exits. All except two. Huang remained behind next to Isozaki, and a female officer walked up to him fearfully.

"How's… Isozaki?" She asked, staring at the blood that was pooling beneath him. As she noted that Huang wasn't bothering to try to stop the bleeding, she started to shake convulsively.

Huang looked up at her with a very tired expression on his face. "I'm sorry. You're husband's dead."

As Li ran further into the building towards his apartment, he heard a loud wailing sound issuing from the ground below. He didn't react at all, but just kept on running.

Suddenly, Li skidded to a halt at a door, and swung it open. "Yin!" he yelled. "Are you alright?!"

A silver-haired, slender girl looked up from where she was slumped on the couch but did not look him directly in the eye. Despite this, the complete lack of emotion on her face was obvious. Although Li's face was fairly impassive most of the time, it sometimes seemed to be concealing some emotion hidden underneath, which occasionally rose to the surface. The silver-haired girl's face was best described as completely devoid of life; an emotionless expression set in stone.

"Li." She acknowledged in a monotone voice. She did not comment on his abrupt entry or move at all from her position on the couch. She merely stared at some point beyond Li's ear.

"You won't need to use that fake name anymore, Yin. We're leaving now." He grabbed her hand, and pulled her after him into the hallway. He started running as fast as he could without making Yin fall over behind him. Yin's head turned towards the general direction of the man's hand, which was holding her's tightly.

Yin nodded. "Hei," she amended as she tried to keep up with the man dragging her down the corridor. "Where." It was a statement, not a question.

"Don't know. They're sending in the state alchemists, so we just need to get far away first."

"Hei," Yin stated. She seemed to be trying to get his attention.

Hei didn't respond, but turned at the next corner, which had a long corridor at the end of which was a large window.

"Hei. What's wrong."

Hei's running faltered for a second, and he looked back her, a look of mild surprise on his face. Yin just kept staring at their interlocked hands.

Hei turned his head back around, and sprinted even faster towards the window at the end of the hall, dragging a stumbling Yin after him. "Nothing."

"You're lying."

They had reached the end of the hall, and this time Hei ignored her. He crouched down. "Get on my back. Make sure you cover your face; I'm going to have to break through the window."

Yin nodded and put her arms around his neck, burying her face in his shoulder. Hei stood up, smashed the window with a running kick, and fell out the window. He reached for the wire snap-hook on his belt, threw it so it attached to the nearest balcony as he fell. He managed to slow his momentum some, but then the railing his hook had attached to snapped, and he slammed into the ground with considerable force.

"Ugh…" Hei groaned. He remained squatting on the ground for a moment as he wrestled with the pain coursing up and down his legs. The railing clattered to the ground behind him, and glass shards rained down on him and Yin. Because of the broken railing, he hadn't gotten enough momentum to clear the glass… He slowly got up and assessed the situation. He had sustained several cuts, but nothing too major. "Yin, are you ok?" he asked, looking over his shoulder.

"Yes," Yin replied emotionlessly. She was also covered in shallow scratches, but there was a particularly nasty piece of glass embedded her arm that was bleeding badly. Hei looked closer at the cut, pulling her arm towards him. Yin didn't flinch at the pain; her face was still stoically set in stone.

"It'll be okay if we can bandage it soon," Hei determined with a quiet sigh. It could've been much worse. "I'll get out the glass once we get to a safe place. Let's get out of here."

"And where do you think you're going?" A smug voice asked.

Hei whipped around to see a uniformed man, a colonel, as Hei could tell from his uniform, standing behind him. Hei's eyes flicked to the man's pocket. Sure enough, there was a silver pocketwatch in it, signifying his position as a state alchemist. Hei stepped back warily, and was about to put Yin down to draw his knife when he saw she didn't have any shoes. Her feet would be torn apart with all the glass around. He inwardly cursed.

"Colonel Roy Mustang, the Flame Alchemist, at your service," smirked the man. He held up a gloved hand with the alchemy circle for fire inscribed in the fabric. "If you want to live, I suggest you surrender without a fight."

Running was not an option then. The Flame Alchemist would be able to burn both of them badly before they found a place with substantial cover.

"Hei," Yin deadpanned in Hei's ear. "Go. I'll be ok."

Hei ignored her and kept his eyes on the new enemy. Yin fell silent.

"You expect us to surrender to you so we can go be experimented on again?"

"'Experimented on'?" Colonel Mustang quoted in surprise.

Hei blinked once, but continued looking at him coolly. "You don't know about the project?"

"Why would I?"

"All the high ranking officers knew about it."

The colonel contemplated the pair silently. This was an odd criminal for sure. He wasn't abandoning his companion even if it left him completely helpless. And the girl he was with seemed utterly powerless as she clung weakly to the man's neck; the military might have forced a trumped up charge on her to justify her capture. It had been done before.

But, most importantly, this man seemed to genuinely have some knowledge about some forbidden experiments the higher-ups were conducting, and he had seemed truly surprised when Mustang didn't know about this 'project'. Research, huh… Human experimentation was close to the field that the Elric brothers were looking into, in order to get their bodies back. Perhaps… this had something to do with them. And since Major Armstrong had insinuated that what the Elric brothers were searching for, the philosopher's stone, was somehow related to Hughes death… this was definitely worth looking into. Mustang eyed the silver-haired girl. She had to be the one the police report had said would make a good hostage.

As the Colonel stared at Hei and in Yin, in the silence, Hei could hear the drip of the blood from Yin's wound onto the glass surrounding them. He resisted the urge to shift uneasily. If he didn't get the glass out of her and stop the bleeding soon…

"I'll make a deal with you," Mustang abruptly stated. "Equivalent Trade. You tell me all you know about your assassination targets, any corruption in the higher ups, and this project you spoke about, and I'll provide a hiding place for you. However, we'll have a guard on that girl at all times to make sure you don't try to pull one over on us."

Hei bristled at the last sentence, but after sparing a glance at Yin, sharply nodded his head in acquiescence.

"Excellent," said Colonel Mustang with a self-satisfied smirk.

Hei stared frostily right back at Colonel Mustang's smug expression, and thought to himself, If Mustang betrays us, then I'm sure I can find someone who would pay well to have him eliminated.