I want to comment not exactly on white supremacy but the alt-right (and I know gaf will say that they're interchangeable and maybe that's true to an extent.)
Alt-right and anime:
I think that it's because a lot of the current day alt-right lived are pretty nerdy dudes that don't socialize very well. And naturally, they become Anime fans (sorry, but it is a BIT true,) and the world of Anime is really amazing to these dudes. The male protagonists are usually weird and goofy and they always have like 3 curvy ass sexy chicks head over heels over them for some reason. Women in Anime are perfect and cute. They don't have harsh opinions about feminism. Sometimes the chicks in anime are strong, but strong chicks in anime are always flopping their massive tits everywhere and giving every dude a panty shot every 30 seconds so it's ok.
Also --- I lived in Japan for 5 years and I've kind of come to the conclusion that Otaku and Alt-right share a lot of things that are "fan service" for both. Girls are feminine AF. TV shows (even on day-time tv,) zooms in on chicks boobs and underskirts all the time. And it's not like there's a strong feminist revolution that's present. Maybe it's going on somewhere, but you won't find it much online. Now what's "cool" about being white is that you can go to Japan and probably find at least a mildly attractive girlfriend (if you're from a small town in rural America, this girl will be like a 10/10,) and the love and admiration of white people in Japan helps white supremacy respect Asians -- specifically Japanese -- because that is the culture that Alt-right like. In China, I've met a lot of racist , far right Trump- supporters that have soft spots for Asians, because again, Anime, Japanese culture (the Otaku side of it,) and that Asia Asians REALLY look up to white people.
Yeah..........