This is never going to happen going from the firsthand accounts I have heard from non-ethnically Japanese people who are by all accounts Japanese. As in born and raised in Japan, Japanese as first language, Japanese culture, norms etc. Japanese society is simply too racist or xenophobic at its core. If you don’t look ethnically Japanese you’ll never be accepted as Japanese. And that’s even if you are white and even if your partly ethnically Japanese. If you have dark skin you at in for an even tougher time, and any hint of it going back several generations will label you as “the outsider”.
It might not seem like it from the outside because the racism isn’t as outspoken in media as in the US, but imagine spending your entire childhood living with everyone you ever come across acting like you don’t belong to the only country and nationality you have ever known simply because your fathers father was Scottish, it’s rough and a hell on its own.