User blog comment:Xilinoc/Ch. 543 - Letters/@comment-2211792-20130626143149/@comment-5551986-20130627131018

@Sternritter M It may fairly unclear that they might not be related. But still, it hasn't been stated that they were using the word Aunt and Cousin etc as a cover for the marriage, so unless it was stated otherwise they are related. Besides in some cultures present and historical it is and was not uncommon to marry into the same blood related family, par different surnames to keep royal or noble blood pure. Surnames don't mean anything. Kurosaki(F) + Ishida(M) = Ishida child. Kurosaki(M) + Ishida(F) = Kurosaki child.

The woman and child always takes on the surname of the man regardless of family, it is considered honorable and in marriage terms "proper" to do so, although in today's world it differs. Just because my Aunt has a different surname and in 100 years time makes a "tree branch" of relatives of her own, does that make her any less my relative? No, because they still have my blood even if it is but a fraction. Even if the Ishida house and the Kurosaki house have about 4% of the same family genetic makeup, they are still related.

P.S obviously they are not inbred, they just have extremely low matching genes. For instance, if you live on the same continent, chances are you are related to 90% of non-immigrants around, although incredibly distantly, more or less everyone on the planet is. So it could work out.