ATEEZ are an eight-member K-pop group whose blistering live shows and intricate, cinematic sound is shouldering an ever-increasing cache of media praise. Currently, they’re discussing underwear. “I realised after our US tour that I have to bring a lot more,” says the group’s Seong Hwa. “This time, I brought as many pairs as days we’re away.” Seong Hwa is ATEEZ’s eldest member, although in K-pop terms, age is all relative: today is still just his 21st birthday. Later, out of earshot of his bandmates, the blonde vocalist hopes for a cake and celebration on-stage at London’s 2,300-capacity O2 Kentish Town Forum that evening, both of which he gets during the show.

“Seong Hwa is a very special member,” teases Hong Joong, the group’s 20-year-old rapper and English-speaking leader. If someone runs out of underwear mid-tour, do they share? Their expressions freeze. “No!” is the collective, horrified groan.

ATEEZ – comprised of rappers Hong Joong and Min Gi, and vocalists Jong Ho, San, Woo Young, Yeo Sang, Seong Hwa, and Yun Ho – debuted just six months ago, and the mix of wide-eyed thrill and resolve that marks all young idols is imprinted in their words and body language. Historically, though, rookie acts don’t sell out a five-date USA tour, and a month-long run of European dates, in mere minutes. 19-year-old Woo Young, with a little gravel in his voice, attributes their international rise to “luck or practice. But when someone asks why we’re different or special, we always say it’s our performance. We’re great at expressing ourselves.”

One might also point to their infallible chemistry and sense of identity, which amplifies very good pop songs into totally gripping ones. Queasy 90s hip hop synths whine on “Pirate King”, “Desire” houses lush instrumental builds and raw ambition, and ominous doppelgangers stalk “HALA HALA (Hearts Awakened, Live Alive)”, a song in which Hong Joong likens ATEEZ to the Suicide Squad. “In the movie, they’re so unique,” he says. “There’s eight of them and eight of us, and I wanted that kind of impact and meaning in the lyrics.” Their concept – the search for treasure, in whichever physical or emotional guise you wish it to be – flows throughout Treasure EP1: All To Zero and Treasure EP 2: Zero To One, immersing you into their journey.

The day prior to the show, they spend the afternoon shopping and touring Chelsea FC’s stadium. They like London’s atmosphere and springtime gloom. They’re unaccustomed to doing interviews separately. “I’m nervous!” grins Woo Young, and sandwiches his hands between his thighs. They’ve undertaken years of prerequisite performance training within K-pop’s entertainment agencies to be where they are now, although idol-dom wasn’t a decision all their families supported. For most of the members, their agency, KQ Entertainment, is the second they’ve joined; it’s standard for determined trainees to attempt switching agencies, seeking a better opportunity to be picked for a new group.

“My parents were against it, but I wanted to go to Seoul,” says Yun Ho, tall and genial, a 20-year-old whose adult angles are beginning to carve away his baby cheeks. His hometown of Gwangju is nearly 170 miles from the capital. Only after his acceptance into the vocal department of an arts high school did his family relent. Min Gi’s father, a former backing dancer, wasn’t convinced his son had it in him. “When I first started music, my parents thought I’d only last a month. My father told me to prove it, whether it was to join a company or let him hear a song.”

“When someone asks why we’re different or special, we always say it’s our performance. We’re great at expressing ourselves” – Woo Young, ATEEZ

Jong Ho, who at 18 is ATEEZ’s youngest member, has a powerful voice that gives the group an emotionally volatile edge. He trained after school for “five or six years, which were necessary to grow and find myself”. San remembers the daily vocal and dance lessons, clutching his limbs. “Every night, muscle pain,” he says in English, with a gleaming grin. He’s not fluent, but has near-flawless pronunciation. “I wasn’t confident and didn’t know what I was good at. But every morning, (I’d think), ‘I can do it!’ It’s mind over body.”

For Seong Hwa and Yeo Sang, training had an emotional toll. “When you’re a trainee, people don’t compliment you,” says Yeo Sang, hesitantly. “They just tell you to fix something.” As a group, they relied on each other, developing what San terms a “natural synergy”. “We’d be drenched in sweat (in practice) and having a hard time,” says Woo Young. “It’s then we’d get close as friends. It’s hard not to.”

Hong Joong was KQ Entertainment’s first trainee, and their only one for six months. “I’d watched idol reality shows and thought if I was a leader, I’d be strong.” By “strong”, he means “authoritative”, but Jong Ho describes him as “wise” instead. “I like conversations and being gentle,” Hong Joong says. Still, he’s subtly, constantly watchful of the group’s interactions. Between one another, he says, “we’re like (same-age) friends”, bypassing the formality of the hierarchical age and status system which governs South Korea’s general etiquette. “I worry sometimes, because if someone makes a mistake at a show or interview, that’s (not good for) our image. But if I come down strongly, they can’t understand. So I give them chances. I let them learn.”

He’s already the quintessential idol – magnetic onstage, sweet and enthusiastic off. Min Gi’s cut-glass cheekbones and pointed gaze may be intimidating-looking in videos, but he’s generous and affectionate in-person. San and Woo Young’s devilish stage presence dissolves into boyish camaraderie. Growing up, Woo Young was so energetic that “my mum said she couldn’t concentrate. I’m trying to become more mature but, half jokingly, I tell the members I’m going to remain childish until I’m 23.” He is a dichotomy. They all are. With countless fan-created video compilations and memes dedicated to capturing such contrasts, duality has become a highly celebrated part of K-pop’s DNA.

Forming an idol group is as much scientific as intuitive. They must be unique individually, but stronger together; their backgrounds and personalities should differ, yet perfectly complement each other. Idols are expected to be paragons, so it’s commonplace for innocuous, random skills or habits – like Jong Ho’s ability to split apples bare-handed, or Seong Hwa’s cleaning jags – to be played out over and over, somehow becoming intimate personality traits. But as interest in idols grows internationally, the barrier between artist and fan is cracking with a need to connect in deeper, more authentic ways.

ATEEZ are using all the social tools at their disposal. They’ve been on the live broadcasting app, VLive, almost nightly since being on tour. Is there a line to be drawn between taking care of yourself and being ‘on’? “After we perform, we’re tired and the fans know,” says Seong Hwa, “but it makes us happy to communicate with them in our everyday lives. We don’t really hide anything.” Seong Hwa speaks carefully, but at length – which is surprising, given he’s not been known for being voluble with the media so far. “There’s a difference in what’s shown and what it’s like in my personal life,” he puts it simply. When he’s off-stage, Seong Hwa says, he talks as much as San (who refers to him as a “backstage moodmaker”) and Woo Young.

Yeo Sang has a discernibly soothing presence and, like Seong Hwa, is often reticent on camera. Woo Young calls him playful, a listener, his best friend, and claims they can finish each other’s sentences. His mother was a teacher and ran a strict household. “We’ve had to get ATEEZ's name out there, but my personality is the total opposite, so I worried a lot,” he admits. “I tried to talk more than normal and worked really hard to fix my shyness.” That tenacity is evidenced by the finger splint he’s wearing. In America, his ring finger went in the opposite direction to his hand on the floor when dancing. Terrified it might be broken (it wasn’t), yet unwilling to stop the stage, he gritted his teeth, popped it back into place and completed the show, his hand swelling like a balloon.

“I don’t think we’re famous yet. We feel that many love us, but is that being famous?” – Hong Joong, ATEEZ

Their wary skittishness of bringing me, a newcomer, into their inner circle, is brief – ATEEZ can’t not be ATEEZ for long. It’s Min Gi cheekily shooting us finger-hearts during a fansign, and Yeo Sang’s friendly attentiveness. It’s Seong Hwa’s story of getting entangled in his necklace and ripping free before the TV camera swung back to him, an incident which ignited both a disappointment for failing to be perfect and a realisation of how intensely he loves his job. It’s Hong Joong revealing he’s no longer sensitive of his slight hands thanks to fans altering his self-perception, or Yun Ho laughing as he reenacts trying to find the right camera at music shows, and admitting they feel empty when not together. It’s San turning out to be an avid reader of thriller and mystery novels, and Woo Young and Jong Ho leaning over an outside balcony to check out the line, then running away from the screams, giggling.

They grew up watching idols, pursuing a place within their ranks despite understanding how tough the industry can be. Min Gi knew the only way he could both dance and rap as a career was in an idol group. Jong Ho wants to bring hope and confidence to people. “Being an idol is a hard occupation,” agrees Woo Young, astute behind his giddy energy. “When I was younger, I’d think idols were so cool. They were someone’s role model, and I wanted to be like them.”

But fame is powerful and painful, and ATEEZ, who diligently comb social media, are somewhat aware of that. “We see the feedback, replies and reactions – if it’s good, then I enjoy it,” says Woo Young. He’s not blind to the negative comments. “If it’s too strong, I try not to take it to heart. It’s very important to control your mindset.”

Hong Joong squirms. “I don’t think we’re famous yet. We feel that many love us, but is that being famous?” Mention a pre-debut performance that recently surfaced on Instagram and he laughs, embarrassed. “It’s not me!” he jokes. San overhears and needs a detailed description of his leader dancing with a girl, flower in hand. Hong Joong looks like he wants the Earth to swallow him. There’ll be many more moments where people make their past public or criticise the present, but Hong Joong desires fame nevertheless. He believes in the strength of ATEEZ’s concept and wants it to spread worldwide.

Success and industry recognition, however, are separate, and Woo Young is conflicted. “I don’t think we need awards to be recognised. But there are awards many senior artists have received and we practice hard thinking it’d be great if we could win those.” Jong Ho, consistently unflappable, is staunch. “I don’t want our success determined by how many albums we sold or views. This is something we began because we like it.” San is equally pragmatic: “As we grow with each release, I think, more than any other award, that will be the biggest reward.”

ATEEZ have spent so long together that they often echo the same sentiment, but their visions of the future are more singular and revealing. Yun Ho wants to “continue like a family”. Ask Seong Hwa if he wants ATEEZ to be the world’s biggest group and he takes a modest line: “We’ll have good results if we do our best with what’s presented to us right now.” Hong Joong aims highest, motivated by BTS’s own aspirations. “A Grammy award,” he says. “The Super Bowl halftime show.” His eyes are glowing, but the keen hunger is tempered with a little practicality. “If we can’t get there we won’t regret a thing,” he adds, with a quick laugh, “but we’ll always try.”