There comes a point where you really shouldn't have to be bothered to consider what those in another country will think when your product is primarily aimed at the domestic market. Different countries have different values and we have to accept that. OPM was a web comic written for the Japanese audience that happened to capture the interest of foreigners. ONE shouldn't then be obliged to appease those who chose to read it. If he suddenly does something you don't like based on your own culture then that's just life, clearly for him (and I guess most of Japan as these elements have gone unchanged with a redrawn manga and now an anime adaptation) these are non issues.
In Britain we had a prime time comedy on the BBC called Come Fly With Me. This show featured characters almost entirely portrayed by two white men, including black, Japanese, Pakistani etc. Now I know that this type of thing would be a big no no in America, but here in Britain is was seen as OK (I should note it got complaints, but almost everything does because complaining about TV is a national pastime). And no, this isn't something from the 70s, Come Fly With Me is less than five years old. I doubt many would say Britain is a country that needs to learn about diversity. Or for another British show written for British audiences that has a reputation of being rather un-PC and yet popular abroad - Top Gear. No one was telling them what was not acceptable abroad.