The characters who've appeared thus far are the types you'd expect to see in a horror/survival story. That's not a bad thing if the characters are fleshed out since those different types are needed for these stories to entertain... but, so far, there have only been a few few short flashback scenes.
There's the good natured guy (he's more Anakin than Luke good, mind), there's the guy who loses it because of the situation (and new psycho characters keep appearing) and there's the damsel in distress. All that's been missing so far is the black guy who gets jumped on by a monster, and that's because the Japanese don't draw black people.
So far, it seems Ako is in the story just to wear tight shorts, get naked from time to time and be saved. I'm not moaning; I'm quite fond of a well-drawn school girls, and it'd be dull if it was a sausage fest, but she's not been a great character.
In the first, underground arc she miraculously evaded being raped and murdered.
In the second, above ground arc she miraculously evaded being raped and murdered. I'm starting to see a patern, and I don't see it changing with the rapist army guy still in the game.
...oh yeah, the rapist army guy. If there's a war/gone to hell scenario, you can almost be sure some guy(s) will discard duty and go woman hunting. As soon as he was shown to be looking at a porno mag with a school girl on the cover, you just knew he'd be the new guy on the block to treat Ako like a "weak girl". (Really, the author seems intent to point out as much as possible that Ako has a weak body; even her introduction had her in PMS mode!)
Trolling: The more intelligent a person is, the more they struggle to detect sarcasm - that's what MAL has taught me. I never actually mean to start arguments - I just like pulling peoples' legs - but people always take things the wrong way. I need to stop upsetting people without intending to... :(