I never heard the accents of in the American version of FF13. I play the Japanese version and they aren't bad. Vanille and Fang just have normal Japanese voices. Fang's voice acting is pretty badass. Vanille is just a normal anime sounding voice, not annoying to me. Just goes to show that poor voice acting can change your image of the same character.
As for most annoying, just about anyone from 12. It was the only FF game I didn't enjoy and couldn't wait to be done with.
As for most annoying, just about anyone from 12. It was the only FF game I didn't enjoy and couldn't wait to be done with.