Tearful and screaming by turn, tens of thousands of BTS fans gathered in Seoul for the finale of the boyband’s lucrative world tour, some flying thousands of kilometres to pay homage to their idols and swell their backers’ bulging coffers.

The septet’s global prominence reached unprecedented heights this year, becoming the first K-pop group to top charts in the US and Britain and performing a string of sold-out shows in Los Angeles, Paris, and London’s Wembley Stadium.

The floppy-haired musicians, all in their 20s and often sporting earrings and lipstick, appeal to a generation comfortable with gender fluidity.

They connect with their largely female fans — collectively known as ARMY — by opening up about their struggles through their music and on social media, which they flood with selfies and personal messages.

“I love them so much and they are one of the most important things in my life,” said Milena Marunova, 20, who travelled from Russia to Seoul for this week’s concert, her voice trembling with excitement.

That depth of engagement is key to their appeal enduring, according to CedarBough Saeji, a specialist in Asian languages and cultures at Indiana University Bloomington, contrasting it to rapper Psy’s 2012 megahit Gangnam Style.

“Psy didn’t have a fanbase, he had one viral hit song,” she said. So when the follow-ups “weren’t quite what the audience was looking for, they moved on. But BTS has many very loyal fans.”

She added BTS’ music was well produced with excellent videos, “and performed by incredibly handsome and charismatic young people”.

BTS Dolls

That popularity has enabled a hugely profitable variety of spin-off products and activities.

Their merchandise ranges from pens and notebooks to pillows and blankets, and they collaborated with Barbie manufacturer Mattel for BTS dolls, which the US toymaker said lifted its international sales by 10 percent.