One coworker asked me about the hardest stuff in heavy metal. I showed him this.
Funnily, despite the very loud opposition of the few lonely defenders of true serious metal they really quickly also managed to become one of the most popular bands in metal.
Actually no surprise since they fulfill all qualifications of a female fronted metal band. Including having a top-league vocalist. And they clearly have a metal attitude in what they do. And its normal in metal if you can't understand the lyrics. And they also appeared on the crucial metal festivals.
It is just really alien, because the band comes from unchartered waters for the typical western person. Maybe the context makes more sense for somebody from Japan. The typical reaction here, when first hearing them, is usually complete disorientation.
One question though might be, how well the phenomena ages: As I understand japanese pop culture, the members of a band are much easier to replace than metal culture likes (just remember Nightwish or Iron Maiden!), living even a bit like Lemmy is unheardof and the age limits are stricter than in modelling. But there are many exceptions to the rule, would be sad to see the voice of their lead vocalist retire already at an age when others barely started in metal.