SAN FRANCISCO — In an era when concert audiences tend to be fairly homogenous, Babymetal drew what may be one of the most diverse crowds the Warfield has ever seen.

Not just racially diverse, though that was certainly true, but diverse in its diversity. There were a husband and wife in their 60s and there was a 10-year-old girl with her dad. There were teens in anime T-shirts and punk rockers in tattered Misfits hoodies. A teen boy in a soccer jersey headbanged while his middle-aged mother sang along with every word behind him. Even among the metal-heads there was diversity; men in pristine Ghost and Gojira shirts stood alongside those in well-worn denim vests with Pantera and Motorhead patches.

That collection of people that one would never expect to come together makes a lot more sense if you know that Babymetal, musically speaking, is a collection of things that one would never expect to come together.

For the uninitiated: Babymetal is comprised of SU-METAL and MOAMETAL, idols who sing and perform tightly choreographed dances in the typical J-pop style, backed by the Kami Band, a group of masked heavy metal musicians. But the saccharine pop vocals and the heavy metal instrumentation work together perfectly because everyone involved is so profoundly good at what he and she does.

That’s not to say the parts were completely separate. Lead singer SU-METAL carried herself with the authority one would expect from the frontwoman of a metal band, and beneath the heavy power metal grooves and blazing metal riffs Kami Band maintained hints of an underlying J-pop sensibility.

The show itself opened with a narrator’s booming voice bellowing, “In the name of the fox god, the sensation of Babymetal continues to spread worldwide. Are you ready to headbang? Now is the time for the metal resistance.” This likely thoroughly confused members of the audience who came with their friends were unaware of what they were in for. Any trepidation immediately evaporated, however, when opening song “Megitsune” began. The band jumped right into a tightly produced, visually spectacular show that managed to keep a stratospheric energy level beginning to end.

Potentially due to aesthetics or the language barrier, there was no stage banter between songs. After each one the room went dark while everyone reset for the next number. But it works, especially when the next song begins with a driving power metal riff like “Elevator Girl” or a series of blazing guitar solos like “Shanti Shanti Shanti.”

It’s almost a shame the Kami Band musicians are nameless and masked; they deserve credit for their contributions. But, like Ghost’s Nameless Ghouls, the anonymity is part of the band’s mystique.

A sort of techno-psychedelic video interlude gave the band members a chance to catch their breath before they launched into arguably their biggest hit, “Gimme Chocolate!!”

As the song’s viral fame launched Babymetal’s American success, it’s no surprise that it got the biggest reaction of the show. What is surprising is how many fans had the choreography memorized.

After few more songs, including hit “KARATE,” it was time for the least characteristic song of the entire show. “The One” is an English-language ballad, sung by SU-METAL alone on stage and accompanied by a recorded piano. It was beautifully performed and showcased her voice, but stuck out because of how downright normal it was after an entire show of tightly controlled and highly entertaining chaos.

The calm didn’t last long, though, and the storm returned with final song “Road of Resistance” and its prolonged sing-along segment.

Opening the show was Swedish melodic death metal band Avatar. A more conventional metal band than the headliner, though not by much, Avatar’s evil carnival theme did a good job of setting the stage for what was to come. That theme extended not just to the staging but the drums, the band’s wardrobe and the sound guy’s top hat.

Singer Johannes Eckerström, a couple songs in, introduced the band simply by shouting “We’re from Gothenburg, Sweden! We’re gonna slap you naked and hide your clothes!”

And that’s basically all they needed to get the point across. Their strangely avant-garde brand of melodic death metal charmed even a crowd as broad as that one, provoking headbanging from young and old alike.

Eckerström sang, screamed, played a trombone solo and drank out of a gas can.

“So many of you are seeing us for the first time,” he said. “I can see it in your faces: ‘Holy shit, what just happened?’ We happened, Avatar happened, you’re welcome.”

But near the end of the performance he had a somewhat odd request. That was Avatar’s last show of 2019, he explained, because the band was going to go into the studio to record new music. And the night before the members decided it would sound very cool if they had a large group of people shout the word “silence,” and the assembled audience was the last large group they would have access to before recording.

“If you don’t give your consent to be on our next album just shut the fuck up,” he said, before coaching the crowd on a few takes of the collective shout.

“San Francisco, I just made you famous,” he said once he was satisfied.

Follow editor Daniel J. Willis at Twitter.com/BayAreaData.