Not sure I agree with any of that, but I do recall that the Aum Shinrikyo cult had some obsessions with the Lost Tribe of Israel theory. I’ve also read that the Aum Shinrikyo may actually be a direct descendant of the “Black Dragon Society”—a pre-WW2 group of Japanese officers and officials that claimed Ainu descent. I am fuzzy on a lot of this, but I do recall that the Society was one of the reasons why Hitler believed there was some racial affinity between Germany and Japan.
The whole race, language, ethnicity obsession was all in all pretty widespread in Eurasia, and extremely popular through the 19th century and to the end of WW2. I don’t know whether the Ainu are actually caucasians or used to be, but I don’t know why this should be surprising—several other central asian groups were “caucasian” (the Ainu are widely believed to be central asian in origin).