[@Vocab]Unfortunately this is my RP and I have my own criteria for characters that I accept:

1) How does he have a surprising amount of muscle? Does he work out a lot? Going off the sterotypical otaku even by anime standards, they don't live very active lives. Sure he might not be fat or anything since he might just not eat a lot or have lucky genes, but you don't build muscle nor stamina by watching [i]Love Live[/i] all day.

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2) How does he get the money for not only his daily living expenses, but also otaku merchandise and blackmarket weapons? I'm doubtful that he'd be able to procure a weapon on his own as he doesn't appear have any sort of bank fund to go off of or even a job. That's also not considering that since the government had meddled with his family before hand, there's good chance they'd be keeping tabs on him and also a chance that they'd get a little more than pissy if they found a 18 year old kid buying blackmarket stuff. He'd most likely also just go to flat out jail since he's legally an adult.

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3) His skills, I can get behind that he knows both English and Japanese and that he knows his way around a computer, but the rest is very questionable. Like I've stated before, otakus don't live very active lives, and it sounds like Mastu here is in the military. Ignoring how he would get guns and ammunition, he would have no way of training himself to shoot without getting someone's attention and most likely getting himself arrested too. As for bladed weapons, sure he could have just practiced by swinging a kitchen knife around, but that by no means an "expert level". 

I can also presume that he has never been in a fight or enough fights to be said to "know his way around a fight" unless people now considering someone getting beaten by their mother to be "fight experience". As for his knowledge about the body, I can write that off as him just being interested in anatomy but knowing what parts of the body are weak and being able to exploit that knowledge in the heat of the moment are two different things. His acting skill I can see as being part of his mask he wore daily so people saw him as "normal" however.

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4) About his bio, I have no qualm about him being both a genius and an otaku as people can be naturally smart and its also a trope in anime. However, him "collecting anime and manga stuff" harkens back to my point of where does he get the money? You also said that he's living and government subsidies do not give enough money to buy both basic living expenses, otaku stuff and blackmarket weapons.

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5) The last point in your Misc. section, if Matsu has [i]that[/i] many mental illnesses and suffered from depression for [i]that[/i] long, there is no way the government would have let him live on his own. He would most likely be put in a mental hospital or at least kept under supervision and forced to make frequent trips to doctors, neither of which help his case about trying to get weapons.

EDIT: Remember when I said I can be a hardass and really harsh? This is what I was basically talking about.