Typical kid, typical home. Everything about Yuuma Nakano started out as completely normal. Yuuma's father, Takumi Nakano, was the owner of a well-off textile company that he had forged into a booming business with his own blood, sweat, and tears. Yuuma wanted no part of it, and was fine with his younger brother taking over. Souta Nakano (his younger brother) had a head for business, understood the procedure by which the cloth was made in the company, and was fascinated by it all. But Takumi insisted that the elder brother should be the one to take over. So he began preparing Yuuma for the running of the company.
At a very young age, Yuuma was expected to begin learning the things he would need to run the company. He never once thought that Yuuma wasn't really appropriate for the job— or that at eight, maybe he wasn't ready for that kind of responsibility. Takumi just kept pushing. Three things can happen to someone when another person keeps pushing them. They can eventually learn to push back, they can go where they're being pushed to, or they can break under the pressure. With Yuuma… it was the third.
It happened when he was about thirteen, during a public speech he was supposed to give about the future of his family and his father's company. Though "public" in this case only included his immediate family and a few of the higher-ups of the company. These sorts of things were routine Takumi to put his oldest son through; he thought his employees should get to know the one who would be the face of the company when he passed. At this one, though… the stress got to him. He had spent two days composing the speech, had not slept the night before, and had not been able to eat that morning because he was nervous.
When it was time for the speech, he went out to the podium and put his notes on it. He cleared his throat, looked up… and froze. All of the people gathered were starting at him. His heart raced, his hands shook, his stomach twisted into knots. He couldn't speak. Could barely breathe. And suddenly it became too much.
He fainted at the podium.
It was an utter humiliation. Not only had he let his father down because he couldn't do the speech, some of the people there began to question why Yuuma had fainted. Had Takumi done something to him? So after that, Takumi Nakano was under greater scrutiny. Which was the first thing Yuuma heard from the elder Nakano when he woke from his faint. This too he placed on Yuuma's shoulders, that it was Yuuma's fault that his stockholders were re-evaluating their partnership with him.
All this just pushed him farther into himself, and Yuuma withdrew from everyone. He stopped speaking. And quickly became the last person Takumi wanted to run the company. Souta stepped up in Yuuma's place, and Yuuma was grateful to him for it. As is generally the way, when one becomes a dirty little secret, the easiest way to deal with them is to sweep them under the rug, so to speak. He wasn't going to be killed, no. He would be shipped off to the States.
Takumi Nakano owned a small brownstone house in New York for when he went to the United States on long business trips. He hardly ever used it. So he hired someone to look after Yuuma in the new house (because in the United States and child could not be left completely without a legal guardian until they were 18), and went through the procedure of getting Yuuma a passport to the United States, enrolled in a school, etc. When he got to the United States, Yuuma got settled into his new life as best as he could. Misaki Nakahara had been the one Takumi hired to look after Yuuma in the new place, and she became his legal guardian.
Yuuma had not spoken a word since the fainting incident. Because of this, school proved to be a challenge. He was placed with 'special needs' students— much to his father's chagrin— and instructed in sign language. Academically he did well. Socially he didn't. It wasn't that he was bullied; he generally just plain didn't even acknowledge bullies. Instead of hanging out with friends, he began working with computers. Computers didn't expect anything from you; they just calmly waited for input.
He did have a few friends, mind you. And they turned out to be musicians! One of them took a liking to Yuuma and decided to teach him about the keyboard. Here Yuuma found something else he liked… music. He took well to the keyboard. Even played in a band a few times. He stood in for a missing drummer— his keyboard could make percussion sounds too.
His powers first manifested when he was seventeen. He was trying to look at a friend's computer, because he knew a little about some software that the friend was having trouble with. But the software wasn't working as it was supposed to. In frustration, he said mentally 'Dammit, WORK!'. And it did. He soon found that he could do this anytime he had a problem— just mentally tell the computer to work properly, and it would. And not just computers. Anything technological, he could touch, and "talk" to it.
Another power manifested during the same year, when a bully decided he was going to get noticed. He accosted Yuuma in a secluded classroom and began to hit him. Frantically Yuuma reached for his phone— he intended to use the phone's alarm function to get help. But a burst of electricity exploded around him and left the bully incapacitated, and his phone was dead. He would say after this that the bully broke the phone and it malfunctioned while he was trying to use it. But after that the color of his eyes started to lighten, until they were the yellow color they remained.
Fortunately all this happened during his last year of high school. Of course, in the United States, college preparation isn't done in high school, and the student has to pay for it. Yuuma had the money, but it wouldn't last if he went to school full-time. He didn't want to be overburdened with student loan repayments forever. So instead he looked for a job, to save up the money for college. In the meantime, he looked into some online courses to expand his knowledge. What in? Computer sciences, of course.
Except suddenly… he was not in his world anymore. Yuuma looked outside one morning and the city wasn't there. Misaki was, thankfully— he assured himself of this before anything else. He didn't know what happened. He didn't know where he was. His plans for higher education were put on hold; now he had to learn how to survive in this new world.
Social anxiety disorder is hard to manage. Especially in a culture like Japan, which not only asks so much of its people, but in which such mental problems are rarely acknowledged and almost never treated. It's "the same thing expected of anyone", why would it cause mental problems? Due to the demands placed on him at this age, with no preparation, Yuuma is a withdrawn and unhappy young man.
Only partially because of his upbringing, the rest is because of his social anxiety disorder. He feigns being disaffected by the world around him, as that seems to help him cope with the fact that OH GOD THERE ARE PEOPLE AROUND HIM! Adding to that, Japanese men seem to be somewhat restrained where showing their feelings is concerned. With these two together, it makes for an outward appearance of stoicism.
Goes without saying, given he's mute. But it isn't just that he doesn't talk. "Quiet" is something he does. His very presence is generally low-key and unobstrusive. He is easily ignored, and that's just the way he likes it. It can make it difficult for him to get noticed when he needs to be, but he so rarely wants attention on himself that he can usually deal with this.
Believe it or not, even as much as he ignores people, he does care about the condition of his fellow man. And once you've made a friend of him, he will do anything for you, if it's in his power. EVEN TALK! Well… try to, anyway. He's not one to show it, mind. Japanese men just don't do that. But if you know him well enough for him to care about you, you know him well enough to pick up the clues anyway.
Yuuma can count his real friends on one hand with a couple fingers missing (he has all his fingers, mind). But there's a reason he doesn't have many friends. He's very secretive, and doesn't reveal much about himself. It's hard to tell whether he's just being careful— because you never know who's going to be an axe murderer these days— or whether he's actively pushing people away.