Notes:
The reason behind dust phenomenon:
I wanted to tell you the reason why both Killua and Alluka/Nanika turned to "dust". First, it wasn't really dust just looked like it, in reality, their bodies split into subatomic particles. Then those particles surpass the speed of light, allowing Killua to travel in another dimension and afterward going a few seconds back in time to the point before his body broke apart. As a result, Killua's body re-materialized. As for Alluka/Nanika, her particles followed Killua's and spread to the MHA dimension. Complicated i know, anyway I got the idea from another anime called Fire Force and it's based on one of the protagonist's powers (Shinra Kusakabe) Adolla Burst.
Naomasa Tsukauchi, one of the best detectives and most hard-working in the police force of Musutafu, finally, after months, had a day off, a rare thing for him, but that made it even more enjoyable.
But even on his day off, he chose to work.
He had received a call from All Might telling him he and Eraser-head found a kid close to UA, badly injured and half-dead. They took him to the hospital and couldn't trust any other detective with his case other than him. Afterward, he talked with his head doctor, Dr. Grandeeney Marvell, and asked her to send him his medical file, and any information they found on him. Unfortunately, the only thing resembling an ID was in another language. Eventually, he told the doctor that he would like to talk to him after he woke up. He went back to his office in the police department and opened a new case file.
Name: Unknown, age: Between 13-15, quirkless, injuries: Three broken ribs on his right side, a deep stab on his shoulder, and on his left side a stab wound between his fifth and sixth rib, luckily it wasn't as deep as the stab he had on his shoulder. The boy also had multiple scars throughout his body that dated back to at least ten years, his newest scars were about four to five years old.
His physique was another story, for someone his age, he had incredible muscle mass that indicated hard training. But that was all the more worrisome, why would a quirkless kid need training? His mind went immediately to child abuse, and who wouldn't have thought like that? The boy had multiple scars on his body that traveled way back. If that wasn't child abuse, then what was?
He knew this would be a hard case. He just hoped the kid would cooperate. It was dawn when he decided to pack his new case file and go home to get some rest. After he wakes up, he will go to the hospital and talk with the boy. Of course, that's when he received a call from the hospital telling him the boy had woken up, but it would be better if he could have some rest because of his injuries.
Detective Tsukauchi: "I thought you said that he would be sleeping until afternoon." He said to the nurse who called him.
Nurse: "He was supposed to. We didn't expect him to wake up so soon. Dr. Yamamoto is examining him right now, and later in the morning, Dr. Marvell will take him for more exams."
Detective Tsukauchi: "In that case, inform Dr. Marvell that I'll talk to him after she examines him." He said and ended the call. "Well, it looks like my eight hours of sleep turned to two."
Killua gazed out of the window as the bright light of sun rays entered his room. His expression was blank, hiding his feelings that strained his heart, locking those feelings away, and feeling the emptiness taking over him. He knew better than to let it control him, but right now he didn't have the strength to hold it back. Maybe one day he would, that is if he could find the light he had lost, the light he found in his best friend and his little sister.
He took his attention away from the window and stared at the TV. It had been a few hours since he had woken up, during those hours he learned things about this world, such as quirks - a horrible terminology in his opinion, but whatever, this world wasn't his to care so much about. He learned that quirks are the powers that people possessed in this world and that 80% of the population was in possession of one. The world was also separated into four categories of people: the Pro-heroes, the villains, the vigilantes, and the everyday folks.
Pro heroes were the people that used their powers for saving people and doing good things. Of course, that was a load of crap. Heroism was a job, people got paid for doing what's right, and also gained fame, making them some kind of celebrity. People called those guys heroes and Killua called them hypocrites. Even so, he believed that there were exceptions, maybe All Might - the guy was everywhere on the news and he didn't seem the kind of guy that cared so much for material things such as money, but he was annoying with that freaking smile on his face all the time.
Villains. They used their powers for destruction and catastrophe, maybe some were just misunderstood, some he believed to be simply nuts that loved the chaos and death. "My family would love these nutcases," he thought.
The vigilantes were a different story, they did the job of heroes without expecting any thanks, money, or fame in return. But they were also despised by most people, and the reason for it was because they didn't have a pro-hero license in their possession, making them "illegal", when in reality they did the job of the heroes better than them. After all, part of being a real hero was not expecting something in exchange. Of course, a little bit of gratitude would be nice, but they didn't even receive that.
Lastly were the normal people, with quirks or without. They could be doctors, police officers, garbage collectors, teachers, etc. Basically people with normal jobs.
From what Killua had seen on the news, this world was peaceful in comparison with his own. Here they had villains who would cause destruction for a little bit of attention, while in his world they had a group of criminals that would cause a genocide for money. The Phantom Troupe, they had killed Kurapika's clan, making him the sole survivor of the Kurta clan, and all of this for their eyes so they could sell them and make a fortune. Memories of his blonde friend filled his mind, making him feel sad at the fact that he would never see him and the others again. "This is for the best, now they won't be in danger just because we became friends," he thought, trying to push away his memories along with his sadness.
He closed his eyes and took a deep breath, trying to calm himself. Suddenly, the sound of heels made their way into his ears, whoever that woman was, she was coming closer to the room he was in. The door opened and a beautiful woman with long curly ivory hair and blue eyes that were clear as the sky entered the room. The woman looked at Killua and smiled softly at him. She reminded him of Bisky, who portrayed a cute little girl while in reality, she was an old hag, a terrifying old hag, and the proof of the old saying that appearances can be deceiving. The doctor, on the other hand, portrayed the kind, loving doctor with a calm attitude, while she was indeed kind (at least that's what he wanted to believe), she was also irritated and definitely not calm.
Dr. Marvell: "Good morning, young man, my name is Grandeeney Marvell and I'm one of the doctors assigned to you." She said in a soft and gentle voice, still wearing the small forced smile on her face. Killua stared at the lady in front of him, eventually giving her a small nod of acknowledgment. This small action of his made the doctor misunderstand the young boy's intentions, confusing his silence with arrogance. Still, she tried to keep herself composed.
Dr. Marvell: "Can you tell me your name? Calling you 'young man' doesn't feel right, and also, I would like to avoid calling you 'John Doe'." Killua kept looking at the woman's eyes, looking for something that he himself wasn't sure what it was.
Killua: "Killua." Was his only reply. He broke the eye contact and looked back at the TV, trying to ignore the woman.
Dr. Marvell: "Well, nice to meet you Killua, but is it possible to tell me your last name as well?" The boy remained silent as he watched the news. The doctor sighed, reminding herself that the boy was found with serious injuries and needed some time. She glanced over at the small table beside the bed, noticing the untouched food. "I see you haven't touched your breakfast yet, is it not to your liking?" Silence, once again. "Keep calm, Grandeeney, he's just a boy." "Okay, Killua, I'm going to examine you and after we're done, you will have to answer some questions."
The boy remained silent but took off the shirt that was given to him, so the doctor could examine him.
After one and a half hours of examination, the doctor left and a man in his thirties entered the room.
Man: "Hello, my name is Detective Tsukauchi and I'm here to talk about those injuries of yours." Killua stared at the detective with a blank face, as if he would ever tell him he was from another world or who he used to be.
Killua: Name's Killua. He said with a deadpan expression.
Detective Tsukauchi: "Last name?"
Killua: "Zoldyck."
Detective Tsukauchi: "How old are you?"
Killua: "Fifteen."
Detective Tsukauchi: "How old are you really?" Killua looked at the man quizzically. True, he wasn't fifteen yet but he would be in a few months. How could this man know? "Sorry, I should have told you what my quirk is. It detects lies."
Killua: "So, you're a walking lie detector. This is bad, but I don't really care. I'll answer the simple questions and just ignore the rest."
Detective Tsukauchi: "Technically, yes. Now how about the truth?"
Killua: "Fourteen, soon I'll be fifteen."
Detective Tsukauchi: "When?"
Killua: "July seventh."
Detective Tsukauchi: "Where are you from?" From another world, Killua thought and chose to remain silent. "You speak our language with ease and your characteristics match as Japanese, but the language on your papers is different." Once again, Killua remained silent, while the detective was curious, he chose to let it go and move on to his next question. He could always ask him later. "I was told you are quirkless, is it true?"
Killua: "Yeah." Finally, an answer, the detective thought.
Detective Tsukauchi: "Then how did you pick those up?" One of the heroes that found you said that they are quite heavy." The detective said while pointing his finger at his yo-yos. Killua looked at them and tried to think how to cover for that, without lying.
Killua: "I'm just strong." Tsukauchi looked at the boy in front of him. He was told that those yo-yos weighed fifty kilos each, but it was true he didn't have a quirk. Both the medical examination and his own quirk confirmed this. Despite not having a quirk, the kid could carry 100 kilos around like it was nothing. That doesn't make any sense. "Just how strong is this kid?" The detective thought.
Detective Tsukauchi: "How much weight can you lift?" The detective asked mostly because of his curiosity. About 20 to 25 tons, but you don't have to know that, Killua thought while giving a blank stare to the detective, choosing once again to remain silent. "I'm guessing quite a lot based on your silence. Anyway, let's get straight to the point, how did you get those injuries?" Once again, silence. "How about your scars, mind telling me how you got them?" This time, Killua just turned to face the window, refusing to answer him. "Kid, work with me here. From what I've gathered, those scars came with a bad background such as child abuse." Again, silence. "What about your parents, where are they?"
Killua: "Away..."
Detective Tsukauchi: "Care to elaborate?"
Killua: "Not really."
Detective Tsukauchi: "Are you a villain?"
Killua: "No." Killua replied without hesitation, it was true he wasn't. Not anymore.
Detective Tsukauchi: "What about your parents?" Silence filled the room once again. The detective sighed and spoke. "You do realize that the possibility of a foster home or an orphanage is quite big, right?" He didn't get a reaction from the boy, as he kept staring outside the window. "All right, we will stop for now and continue tomorrow. For now, get some rest."
Foster home, huh? The boy from another world thought as he kept his stare out the window, watching the life of this new city and the clear sky. Gon would love this place.
As the detective went outside of Killua's room, he pressed the first name in his contact list. He waited no more than one beat for the other side to pick it up.
Detective Tsukauchi: "Hey, I just talked to him. He didn't answer most of my questions so he still remains a huge mystery. It would be great if you and Shota try to talk to him, maybe he will elaborate since you are heroes."
Other side of the call: "Sure, we'll give it a try. Did he tell you about his scars or how he got injured?"
Detective Tsukauchi: "Nope, he only told me his name, age, and birthday."
Other side of the call: "What about his quirk? I know they said he doesn't have one but..."
Detective Tsukauchi: "I asked him and he said he's quirkless. And when I asked him about his yo-yos, he simply said he is just strong."
Other side of the call: "Strong he may be, but it's unnatural for a kid his age to be this strong."
Detective Tsukauchi: "Like I said, he's still a mystery."
Other side of the call: "One we need to solve."