In any great pop show, there should be a moment when your jaw and heart rate drop in unison because of the sheer insanity unfolding in front of you. A BTS concert has about six of them.

Scattered across two-and-a-half hours of sugary pop ecstasy, they arrive in waves. The sight of 20,000 globe-like bulbs bouncing in sync around London's O2 Arena; a complex dance routine, executed with such agility that you'd think the band came into the world wearing tap shoes; lurid fireworks, fizzling into smoke across a crowd of enchanted and screeching sweaty teenagers.

What we’re witnessing is music’s most potent new craze: BTS, the Korean leaders of pop’s painfully cool boy band renaissance. A die-hard fan once described their followers as "Directioners on crack" – and they weren’t wrong. This seven-piece ensemble have been breaking records in the West thanks to their brand of admirably pure pop, hidden beneath subwoofer-shattering dance beats. Young fans around the world are hooked.

BTS are the first Korean act in history to headline a British arena, and they have no intention of letting that chance go to waste. With the exception of the band’s baby-faced member Jungkook, who injured himself before the show and is forced to remain perched on a stool throughout his numbers, the group skilfully dance and sing their way through a near 30-song set list of fan favourites and album deep cuts.

Songs like "Fake Love" (the first K-Pop song to crack the Top 10 in the US) and the explosive opener "Idol" (YouTube history’s most-watched music video in 24 hours) leave your eardrums reverberating as though they’re about to burst, while the more ballad-led moments like "The Truth Untold" allow for some much-needed respite during a gigantic show.

If there wasn’t a fanbase demanding it, a 150-minute show might seem a little baggy for an act who released their debut album just four years ago. But there’s something about BTS's genetic make-up as a band – part Michael Jackson, part Spice Girls – that allows them to get away with it. The show hits its halfway mark and you realise that, while fatigue might be getting to you, the stars on stage are a dab hand at handling such a mind-bogglingly large show.

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BTS call their loyal fans the "ARMY", and there’s a militancy to their tightly structured performance; one that feels so alien compared to the almost messy nature of their predecessors. Barely a beat seems to be missed, and they’re performing – maybe as exaggerated versions of themselves – every minute they’re on stage. Amplified for our pleasure or not, it’s a glorious image that is beamed into the hearts of a K-Pop obsessed generation (and any straggling doubters in attendance) with each passing song.

Whether a show this mighty is sustainable is another matter. The biggest risk for them, at this point, is the possibility of burning out. Their unwavering investment in the here and now has the potential to help them shatter Western pop’s impermeable wall, and become the first household name pop artist to stem from and sing in their Korean mother tongue.