Have you tried to settle permanently in Japan and get the citizenship? It is almost impossible unless you have Japanese roots
As a matter of fact yes I have and I did it. And I have zero Japanese roots (I am a white born-in-America lived there for 20 years former U.S. citizen native English speaker).
Six requirements (simplifying for the sake of the comment; there are exceptions to the below where it's in fact looser/easier than the below) to be Japanese:
1. Be an adult (defined as 20 years or older)
2. Don't be likely to become a welfare case (have a modest, stable source of income w/ an education & Japanese language level high enough that it allows you can to get/keep a job that will allow you to eat and put a roof over your head). You do not need to be rich or even well off or perfectly fluent.
3. Don't have a criminal record, overseas or domestically, and have no immigration problems (overstaying, etc)
4. Don't have any ties to organized crime or terrorism (domestic or overseas)
5. Live in Japan for five years continuously (not on-and-off) and legally (no immigration blemishes)
6. Legally get rid of your other nationalities (if the other country/countries will allow it)... either before (if country will allow it) or after within two years.
It took about five months for me to gather the paperwork and four months for them to approve me. And it is free. Permanent Residency is not a prerequisite, nor is Japanese "roots" (you can be single with no connection).