I'd have to agree with Zouichi being more of an enigma.
In my opinion, he seems to have a quite a few things hidden under the surface, emotions especially, which we only see in the smallest doses which become greater as the story progresses.

But as for Killy, couldn't that be a personality in itself?

Instead of your average loud-mouthed moron who is nothing in a bad situation, Killy is the softspoken/silent, reasonably intelligent type who can easily turn the tide.
It's one of the reasons I like him.

As for the design of the creatures theory, here's what I found on a site once...


"Nihei says he's joking when he says that he likes drawing those creatures more than actually drawing or plotting the manga."
"If it wasn't for work, I'd enjoy doodling all these characters. " - Nihei