Twenty-five minutes after BTS were due on stage, a message is read aloud to a fidgety arena: “Approximately two hours ago, Jungkook was lightly stretching in the waiting room when he collided with floor furnishings and suffered an injury to his heel … Following the advice of medical staff, Jungkook will take part in the performance tonight, but remain seated without choreography.”

Never mind the questions that this provokes – What degree of stretching? What kind of floor furnishings? – the upshot is that K-pop kings BTS, currently the world’s biggest boyband, are making their UK debut one man down. That still leaves six to be getting on with, however, and it would be a churlish fan indeed who felt shortchanged. The other members – Jin, Suga, RM, Jimin, V and J-Hope – redouble their exertions, putting so much graft into their dancing that by the end of the first song, Idol, they’re gulping litres of water. Perched on a chair on a wheeled platform, and perhaps grateful for the sit-down, Jungkook participates fully in every other way. On the solo showcase each member is allotted, he lavishes the full sweetness of his voice on the mid-tempo pop brooder Euphoria, while he’s a versatile harmoniser on the group numbers, capable of airy heights and sultry depths. Urged on by the fans – who call themselves the “army” – he’s making the best of a frustrating lot, but eventually weeps with vexation.

Sumptuous visuals … BTS at the O2 Arena

Pity also the thousands of army recruits who couldn’t get tickets to this long-sold-out show, and couldn’t afford up to £1,000 charged on secondary sites. Though they could have watched the gig on a live stream, or followed events on social media, where #BTSLondon posts began stacking up as soon as they landed on UK soil on Sunday, there’s no substitute for seeing the Seoul septet in the porcelain-perfect flesh. They also missed out on another matter of importance: the chance to meet other members of the millions-strong army. What fuels the BTS phenomenon is fan-to-fan camaraderie; translated into social media activity, the army’s devotion has kept BTS at the top of Billboard’s Social 50 chart for 95 weeks running.

That nearly all their songs are in Korean has been no impediment to achieving success in the anglophone world – their last two albums were American chart toppers, and the first of those, Love Yourself: Tear, was a Top 10 UK hit. If anything, the Korean lyrics and BTS’s winsome looks, along with a self-acceptance creed that feels like more than just well-meaning sloganeering, create an aesthetic that’s a powerful inducement to their young female following. Two seats away from me, a 14-year-old is singing along, having taught herself the language at home. The other 20,000 people in the room, many shaking £57 Army Bomb light sticks that connect with an app to change colour, are doing much the same. But globalisation works both ways. The foundations of this banging, glittery show have been lifted from western pop/R&B acts, as has their music’s frenetic EDM and Bieberpop.

Two things, though, are uniquely theirs. One is the emphasis on sumptuous visuals; even the dreamy videos shown while they’re changing costumes off stage are so gorgeous they could be art films. The other is the warmth they extend to each other, with constant pats and touches, and to the army. If there’s a message to this show, it is that everyone matters – a commendable takeaway.