The novel's writing is really good and neg diffs 1:39 it's so sad this got axed (due to the weird ass art style). Now we'll never see MC fucking Elena and Martina.
(Elena is his sister, Martina his mother).
Martina is half Spanish, that's why she has the skin color.
By the way there is an actual explanation for foreigners if you read the web novel lore on syosetu, they do touch on it in some chapters on how the history of the world works in universe (it's because in medieval times there was this disease brought back from Africa during the age of discovery(basically the first wave of imperialism) that affected the male population which made men a valuable resource which also caused a butterfly effect which changed the entire course of history. I won't be listing the rest of the history because it's too fucking complex and long, but go onto the syosetu website and read the damn thing for yourself. It's not in the translations of the chapters as it's technically bonus material, but you'll get bits and pieces of it in the later novel chapters). One effect is that this leads to race mixing and makes racism less serious since things are a matter of survival rather than having luxury to just speedrun genocide.
The entire fuckin loredump (it's in Japanese obviously so uh yeah)
Oh by the way MC is special genetically. Or dare I say is descended from someone special by this universe's standards. Possibly other nee-chans.
Do you need to read it to enjoy the story?
Not really. You don't NEED to, but it sure helps add worldbuilding.