I recall you mentioned earlier that Kyouya is fake American just like Klavier is fake German, so I'm curious where this came from? Was it one of the artbooks? (I'm not doubting the veracity, I'm legitimately curious)
I don’t remember if it was ever stated explicitly, or if an interview with the director of GS4 explained it. But it’s heavily implied that he lived in Japanifornia. I know in one old magazine interview with Takumi that his band hit the top of Oricon charts, which is Japan’s top musical listings. That he was later re-introduced to be a student of Themis Academy is just an extra touch.
By the way, it was only in the localized English version where he had an “affected Euro-rock accent”, as the original game script mentions nothing about his actual accent. (I can’t confirm for other localizations, but I assume they jump around with his “foreign” accent.)
So much for that; his VAs for AJ and DD don’t give him any European accent in the English versions…