Thanks for expanding on your question.
I think it makes sense that the demographics are shifting away from homogeneity, as the foreign population is rising and one of the easiest ways for foreigners to get permission to reside in Japan is through marriage. Japan is pretty strict about immigration and its population is already declining, so it seems perfectly reasonable for the percentage of mixed children to increase as these trends continue.
I guess, then, the question is to what extent are we assigning a label or value to this change we're observing. Do you think it's a good or bad thing that Japan is moving in this direction?
@salamat, I'm not sure what you mean about Latin American countries or where you're drawing a parallel... what do you consider to be "pure" families in Latin America?