Might need this to be moved to general discussion or something, not entirely sure it fits. Sorry.

Anyway, I've been working on this comic for... Three years, now. Obviously, I was a 13 year old weeb when I started and it's suffered through a lot of crap. Gary Sue was everywhere and little made sense.

But I never actually started it, just planned it out a lot (which resulted in a lot of admittedly good and complex plot-points and such that I can re-use). Recently I'd been using one of the characters in the UTAU fandom as an avatar for one of the voices I made, and he'd been completely refurbished.
I started to rethink everything, and now I have a lot of backstory and characters refitted to my current not-so-weeb state. The only thing I can't bring myself to change is that it's based in Japan. Ahaha. It's mostly inside anyway, we'll all survive.

But the reason I made this thread is because I still can't decide some things for a main character, so I'd like to ask the general public for opinions.

Would you expect that the mental state of an immortal man (after 4 or so years of little social contact other than a homicidal devil, delivery boys, dead bodies and convenience store workers) be fairly intact? When I say fairly, I mean he's not going to immediately shoot everyone he comes across or be a mute.

Would you think his personality would be more cold towards everyone, or an okay guy (keeping in mind that he was raised by a loving family and has limited internet access)?

He had a passion for education when he was younger, but it faltered in his solitude and depression. Would he still speak in a wise style unsuited for his younger age, or would he have stopped learning so avidly when he got depressed and now he sounds a little uneducated? Would he be overly formal or not formal enough?

This last one is the one I'm having the most trouble with... I want all my characters to have an individual speaking style, and the main characters doubly so. Since one has a Cannon voice, that was no trouble, but this other one is hard to figure out.

Thanks in advance. This thread might be updated with more questions, should I come across them