Yeah, the mirror world app can be worked on with us after your character has been approved. It potentially won't be relevant for some time, considering how many people we may have to get through, which is why it's not too important to worry about right now.

Technically you don't need to read much of anything unless you really want to read every last bit of info about every character. The only "plot relevant" stuff that's happened so far is the initial group having a short foray into the mirror world, but even that could be skipped as long as you pay attention from now on. The real developments are definitely going to be later on.

And there's no need to account for where your character has been till now. Even if we had been through a serious day of school, they could've easily been there in the background. There's nothing they need to have reacted to so far, so you can write up whatever kind of character you want.