German and Japanese immigration law makes no apologies for race.
The German government routinely denies citizenship to Turk families that've lived there for several generations if they can't prove all their ancestors entered legally. At the same time they'll welcome a Russian applicant with a German surname that comes from an area colonized by Prussians a thousand years ago.
It's the same in Japan how they bar descendants of Koreans that were forced to move there as slaves. Germany and Japan; those wonderful people who gave us Auschwitz and Nanking and who call Americans "racists".
If this logic is true, all Poles are eligible for German Citizenship (And so are all French, Austrians, Belgians, ect, ect)