Well, Hulkie boy should look scary, you know? being all green and big and angry! :P And chibis must be cuuuute, that is their whole point! :P....hmmm...even if it is not very useful for a slayer to look too cute..hmmm *ponders*
Oh it's very useful! A slayer who looks "too cute" makes her prey think she can't possibly take them down ... so they don't try hard enough ... they get close and POOF - dusted! And she doesn't even have to break a sweat - or a nail. Hehehe.