Plus we don't know who that background characters is based off. Our only information is that he's from shinsengumi. We don't know who he's based off or referencing and the closest possibly reference if the character is even black is Yasuke. And let's stop treating record of ragnarok like it's an accurate depiction of history.
Plus saying 'all black people need is the same treatment as any other person' would have to mean that black people are acknowledged like every one else rather than ignored. Because if black people were treated just the same as every other person, There'd be more shows with black characters and in turn more black representation. The argument for black representation wouldn't be a thing if black rep was more common just like how Asians want proper and accurate representation in western shows.