FFIX is certainly full of oddball characters...
I'm actually of the (not-so-serious) opinion that none of the main playable cast are truly human. Like, everyday humans with no major physical differences.
Freya, Vivi, Quina and Zidane are non-human by default. But how about the others?

Eiko and Garnet are both Summoners - they have extra organs and brain structures that regular humans lack.

Steiner, unlike other 'human' characters, has no philtrum - the depression in the middle of the top lip - and his mouth doesn't actually have any lips at all. Similarly, his eyes are completely lacking irises.

Amarant - like Brahne, he has blue skin. Actual humans simply don't have blue skin. Then there's the aforementioned gargantuan forearms, which make his gait resemble a gorilla sometimes.

So, no-one who could be considered a 'regular human' in that bunch. Though in Steiner and Amarant's case, I think we're just seeing the side-effects of having several character designers working separately, rather than one consistent style for the final in-game designs. Pity, really - Amano's concepts were bloody fantastic.