It's in a fantastical setting and I don't believe it's supposed to be a standard Japanese name (many character names in the series aren't), so unless there's a official source that uses the romanization "Ouzen", I disagree on this one.
For what it's worth, these are the spellings used in the subtitles of the official English simulcast. I would be in favor of aliasing Regu->Reg and Maruruk->Marulk because the currently used spellings seem to be raw transliterations or guesses.
