But... Spanish ppl is not black xD
WTF DO JAPANESE PPL THINK OF US, I'M LIKE NUCLEAR WHITE
I don't know if anyone else will care about this, but the setting of the manga and the prequel was in Cebu, which was in the Philippines. Assuming that the girlfriend of the protagonist was a local employee or owner of the resort/hotel the protag stayed at, then she's a Filipina. We have brown skin, often tanned even more by the sun because it's hot here, but not all. The Spanish here are integrated in our language, but not exactly the same.
For example, the "me gustas" is "Gusto kita" in our language. But there are also people who are still well-versed in spanish. If it will be geographically accurate tho, the gf-chan is speaking in Cebuanon Dialect.
I just assume that the author have an easier time just using the spanish language for the manga.
So that explains why the girlfriend was dark-skinned and not white, because she was actually a Filipina.