Rap Monster, one of the seven guys in the South Korean boy band BTS, says it was only at the end of 2016 that he and the others realized how huge their band had become around the world.

“Somebody in the company sent me a message: ‘You got No. 26 on Billboard OMG congratulations,'” says Mr. Monster, the 22-year-old rapper born Kim Nam-joon, by phone from Chicago where BTS was set to play on Thursday before hitting Honda Center for a pair of sold-out shows on Saturday and Sunday.

“At first I thought, ‘Ha ha, your humor isn’t really very good,'” says Rap Monster, the leader of the group and its primary songwriter. “We didn’t believe it.”

But as more messages started to ping onto their phones he says the BTS boys realized it was no joke: Their sophomore album, “Wings,” entered the Billboard 200 chart at No. 26 after its October release, making it the highest chart position for any K-pop act — not to mention one that sings primarily in Korean — and offering a bit of foreshadowing for Billboard naming the record the best K-pop album of the year.

Since then things have only gotten sunnier for Rap Monster, Jin, Suga, J-Hope, Jimin, V and Jungkook. In February, “Wings” was re-released in a new edition as “You’ll Never Walk Alone,” and the combined editions have since sold nearly 1.5 million copies worldwide. Music videos for “Spring Day” and “Not Today” were released a week apart last month as well and exploded on YouTube where they’ve currently racked up 59.2 million and 60.1 million views respectively.

“When we heard that and really got that, I was saying, ‘OK, this is going to be a whole other world,'” Rap Monster says of the significance of the Billboard chart success and all that followed. “And I feel like we should do something more, and dream something more.”

This past week they’ve taken a step toward something more, playing their first headlining and sold-out arena dates in the United States, after previously having mostly played on multi-artist billings at KCON conventions held here.

“So many people just to see BTS was really an honor,” Rap Monster says of the opening pair of shows at the Prudential Center in Newark, N.J. “It feels dreamy these days.”

Not, mind you, that it’s been anything like an overnight success or an easy road for him and the other BTS members.

He grew up a top student in his school who loved American rappers such as Eminem and Nas, performing even as he attended high school and eventually catching the attention of BTS future manager Bang Si-hyuk at BigHit Entertainment in South Korea. And though he says he gave up on music when he was 16, lacking confidence in where he was headed, he says Bang encouraged him to stay strong, believe in himself, and sign on as the first to join BTS, even though at the time he wasn’t sure who or what it would end up incorporating.

“I was not aware of the other members,” Rap Monster says. “But I like the company and I respect them. And he promised to me, ‘I will make you do your music and get big someday, so please believe me.’

“So I believed him.”

The other six members soon were selected, each of them bringing different talents on the mic or on stage. Songs were developed by Rap Monster and the other members, with a team of producers working to craft the best music from the raw material, the melodies and beats, that they created.

“Our chemistry is different from other groups,” Rap Monster says. “Everyone has their own points and characteristics. If I’m a bad dancer, a good dancer teaches me. If I’m a good songwriter, I help the others with a good melody.”

We ask the obvious question: Are you a bad dancer?

He laughs and answers: “Yes, I’m a bad dancer.”

Their music is different from a lot of K-pop acts that have made ripples on the American airwaves. They’re not popular because of the novelty aspect of their songs — think “Gangnam Style” by Psy from a few years back. And they’re not quite as bubblegum as a group such as Girls Generation or as eclectic as the synthpop of f(x), the first Korean band to play the South By Southwest festival.

Instead, BTS often aims for that sweet spot where R&B and rap get together, the kind of stuff Justin Bieber might be doing if he sang in Korean and there were six Bieber variations with fashionable hair and eclectic yet unified fashion choices.

“BTS music sounds like it’s from America,” Rap Monster says. “We decide to always watch the trends and watch what’s going on over the world. America’s the No. 1 market in the world so that’s why people in America prefer us.”

As for communicating through the language divide, Rap Monster says that’s partly handled by the group’s wildly enthusiastic social media following: “Fans translate our lyrics and interviews,” he says of a following that has landed them at the top of Billboard’s Social 50 list for a total of 17 weeks since “Wings” dropped in October. “They’re able to say, ‘OK, BTS is talking about us and our lives.'”

And it’s partly addressed through lyrical subjects that express the common hopes and dreams and fears and worries of any teenager or young adult in any country.

“Our lyrics are mostly Korean but we always talk about the young people’s lives and their minds,” Rap Monster says. “There’s something similar between every young person in the world, in America or in Korea. We share something together even if we use different languages or live so far.”

American fans are also the savviest music lovers in the world, Rap Monster says, which made heading out on this brief headlining tour a little bit intimidating at first.

“We actually were scared of performing in America as a solo act,” he says. “Their playlists are the best in the world. I was really nervous for them.

“But after we were on stage our fear disappeared. They’re like everybody, they’re like friends. Singing along all of the lyrics even through the raps. They know how to play, the rhythms and the dances.”

An aside here to share our favorite piece of Rap Monster trivia. You might be wondering whether he spoke through a translator. He did not. His excellent English skills were polished in the classroom but also at home through what he refers to as “a Korean mothers syndrome.”

“‘Friends’ was really famous for the mothers in Korea for English education,” Rap Monster says of the hit American sitcom from the ’90s. “It was kind of like a syndrome. Korean mothers make their kids watch ‘Friends’ even when they were eating food or playing.

“I think it really helped. It has like 10 seasons, I think, and I watched it like more than five times through the 10 seasons. They use the gestures and expressions, like, Americans use, right? I think that naturally teaches me how to speak or how to make a gesture when you try to express some emotions.

“Thank you, ‘Friends,'” he says, laughing. “God bless ‘Friends’!”

Rap Monster recently collaborated with the American rapper Wale on the song “Change,” which like some of BTS’ other songs — and unlike most K-pop — touches on politics and societal issues. He says he’d loved Wale’s music for a few years when the opportunity to do the song came along last year “like a miracle, like a dream come true.

“The song has already come out and we shot a music video together, but still sometimes I lie in my bed and think, ‘Did I really do something with him?'” Rap Monster says.

He knows that boy groups from Backstreet Boys and ‘N Sync to the Jonas Brothers and One Direction tend to have a finite lifespan before members get restless to move on solo projects, acting gigs and other opportunities. But he thinks the variety of interests and musical genres that individual BTS members have can be handled on the side or even within the group, and BTS itself can carry on.

So while Rap Monster says he’d love to collaborate with Drake or Miguel one day, Suga feels the same way about Kanye West and Flume. Jungkook seems more inclined toward pop R&B — his dream musical partners would include Bieber or Charlie Puth. V is a little bit old school, having mentioned Norah Jones and the Fugees as on his wish list. Rap Monster ticks off the rest of the band: Jimin digs Chris Brown, J-Hope is into the similarly initialed J. Cole, and Jin is a fan of old-school showman Bruno Mars.

“I always tell them that every time we have hits under the name of BTS we shine the best when we are a team,” Rap Monster says. “I know all the seven members, they love music, and I know their No. 1 wish is for us to perform and make music and sing and dance.

“Maybe someday someone will want to be on a television show or be an actor,” he says. “I just hope they know all of the popularity and fame and money is from the name of our team. That’s not one person, everybody contributes to the team.

“Nobody knows the future. I just hope it can last as long as possible.”

Contact the writer: 714-796-7787 or plarsen@scng.com