Toji:“Wow, has the class population dropped or what?”
Reichu: And… break out the Kansaiban! Toji's pecular mode of speech gives away the fact that he is not originally from the Kanto region (where Tokyo-3 is located) — he's an Osaka boy.
MDWigs: Most of the original Gainax boys are from Osaka; Takami Akai, Hiroyuki Yamaga and Hideaki Anno were all students of the Osaka College of Art. The Kansai dialect does sound quite different, but it's not that bad, just strange to people from other parts of Japan (think "Osaka" from Azumanga Daioh).
Shin-seiki: I think there's an unwritten rule that every anime has to have at least one character that stands out with a Kansai accent: Think Lum and Ten in Urusei Yatsura, Kero-chan in Card Captor Sakura, Osaka in Azumanga Daioh, Kitsune in Love Hina, Caldina in Magic Knights Rayearth, Innchan in Angelic Layer, Tasuki in Fushigi Yuugi, and so on…
Reichu: English translations often meet the challenge of trying to "represent" Kansaiben by substituting it with an American Southern, mild Ebonics-tinged, or Brooklyn accent. (Source) ADV doesn't really bother and simply makes Toji speak more informally than the other characters, but Viz's translation of the manga goes all out. To be honest, I find reading a Brooklyn accent to be bad enough, and that ADV chose not to have Toji say stuff like "Youze guys" in either of their English adaptations (sub and dub) is something to be commended for.
Incisivis: Tell me about it. I tend to assosciate the addition of "overt" accents with edited anime on TV (British and Brooklyn seem to be popular ones), and because of that, and since it's kind of jarring anyway, I'm glad that didn't happen. To be honest, I can't understand the trend. I think it would be enough to just stumble upon the fact of Kansaiban on the Internet, especially if you don't have any clue why this character suddenly has an accent.