This might surprise you, but Japan has very close ties with fascism. Ever seen the Japanese flag with the rays coming from the center red sun? That’s the flag of Imperial Japan, a fascist terror that scarred much of Asia. Japan refuses to denounce their war crimes, and there are an unfortunate number of reactionary fascists who use the flag of Imperial Japan as a symbol they support.
I’m absolutely not saying that every Japanese person is a fascist, not even close. I am, however, saying that I’m fairly confident that these particular Japanese fans are aware of the Nazi ideology of the bands they listen to, and listen precisely because of that.