‘This must be a breathtaking situation for you,” runs the Monsta X song Trespass, in a rough translation. “I’m gonna be rude and enter your heart / My love knows no manners.” It was their 2015 debut single, released after the seven-strong boyband were assembled on a South Korean reality show, and the lyric turned out to be prescient. For Monsta X’s fans, who go by the collective name Monbebe (“my baby”), the group’s first major London show – an under-promoted gig last January having been quietly forgotten – “breathtaking” doesn’t do justice to the experience of seeing the K-pop princes in the flesh.

Many have slept outside the venue to reserve places in the queue, which stretches hundreds of metres down the road, and they’re so charged up that they erupt into shrieks when a group of fans suddenly perform a creditable Monsta X dance routine in the street. “It’s not about the fact that we can’t understand them [the band primarily sing in Korean]. Their message is deeper than [that of] western artists,’” explains Teniole, a 16-year-old Monbebe who has never been to a gig before. “It’s nice to belong to something.”

Inclusiveness is key to their success outside Korea: this tour called The Connect. Monsta X are openly indebted to the fans, creating a comradeship of equals by frequently addressing them directly, and building Monbebe references into the jokey film clips that play while the group change clothes off stage. The fans do their part by roaring Happy Birthday to group main man Shownu, who turns 26 on 18 June, and singing along to Korean lyrics. The predominantly teenage female crowd, a slice of multicultural London just released from GCSE exams, fizz with joy each time “Monbebe” flashes on to the video screen. Some of the self-absorbed ninnies of western idol-dom might listen and learn.

Facebook Twitter Pinterest Monsta X in Pyeongchang-gun. Photograph: Han Myung-Gu/Getty Images

Korean boybands exist to provide an entertainment package: like the US-chart-topping BTS, Monsta X are equally proficient singers, rappers and dancers, and prove the point by zipping between musical genres. Their core sound is the boilerplate hip-hop and R&B that influences every teen-pop sensation from here to Saturn, but during their show they consistently branch off. Emollient ballads are succeeded by party-starting EDM; a pretty smooch-fest called Tropical Night is countered by Roller Coaster’s propulsive synth-pop. They spend time highlighting individual strengths, with tall, sparky Hyungwon executing a solo dance to Charlie Puth’s How Long, and Shownu and slinky Jooheon delivering a supper-clubby cover of Bruno Mars’s Versace on the Floor. Illustrating that too much is never enough, the song finishes with Jooheon’s gold jacket exploding into a hail of glitter that he’ll undoubtedly be picking out of his hair for the next 24 hours.

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The music is interleaved with lengthy intervals of folksy bantering, much of it translated by an assistant in the wings. At these moments, Monsta X are a septet of Eric and Ernies, reeling off gentle one-liners and sight gags that reinforce the message that humour transcends boundaries. A dominant theme is their love for London: “Harry Potter! Double-decker buses! Britpop!” (Their next date is Amsterdam, where they will undoubtedly find love for bicycles and canals.) They pay tribute to “Britpop” by covering Ed Sheeran, who’s playing a gig of his own tonight at Wembley Stadium, and the Monbebe join in resoundingly. No translation is necessary during this uplifting show of east-west harmony.