I just don’t like the concept of race at all. We are all human, full stop. The concept is useful in understanding the realities of the world we live in with regard to how people are treated based on the concept, and it’s useful for working to fix/mitigate the damage to individuals and groups based on it. Other than that it is make believe and only serves to separate us based on make believe stereotypes.
Edit: I read about “double race” on Wikipedia, and if I understand it correctly, it has more to do with culture than with race in concept, but I still have reservations about splitting people up into broad categories and viewing that as an absolute.
BTW, I’ve been to Japan many times and they are not wholly welcome to outsiders, so I don’t know that I would base anything on that part of their system.