EAST RUTHERFORD, N.J. -- Their name is just three letters, but they spell out a worldwide phenomenon that's landed in the New York metro area in a huge way.

BTS, the K-pop super-sensation, will take the stage this weekend at MetLife Stadium for two long-sold out shows, but this whole week, BTS mania has seized the region.

Long before sunrise, lines of BTS fans -- who call themselves ARMYs (an acronym standing for Adorable Representative M.C.'s for Youth) -- were on hand outside MetLife Stadium. The fans weren't there to get good seats, since admission to the MetLife concerts is through assigned, pre-purchased tickets. They were on hand to buy BTS merchandise.

"We woke up at 4 in the morning to get ready to be here," said one ARMY, who'd driven in to the East Rutherford stadium from Rochester, New York, 330 miles away. She and her friends arrived well before the stadium's merchandise pavilion opened at 11 a.m., "because the lines get crazy. Crazy," she told PIX11 News. "We went to the [merchandise store] in Chicago last year, and by 11 a.m., everything was almost sold out."

The MetLife concerts are the culmination of a week of activity by the seven-member band. They took their act of singing, rapping, and songwriting in Korean and English to the Central Park Summer Stage on Wednesday for a Good Morning America appearance. Then, on Wednesday evening, they were musical guests on "The Late Show with Steven Colbert" at the Ed Sullivan Theater. The megagroup is also famous for its tight dance moves, which were on display at both venues.

Meanwhile, across the Hudson River from MetLife Stadium, in the Chelsea neighborhood of Manhattan, another BTS-related venue has been set up since early this week. The BTS pop up shop, across the street from Chelsea Market, has a concert-like feel, from the line outside, to the party inside, with ARMYs singing to the videos playing on the wall-sized flat screen display, and taking selfies in front of the step-and-repeat emblazoned with images of the seven young men from Seoul.

"It's my birthday," announced Mary Savino, who'd come to shop and have fun with her daughter, Courtney, who added, "It was my birthday on the 15th. We came to celebrate it with BTS!"

The Savinos, from New Milford, Conn., joined the hundreds of people who filter through the store each hour from all over the country and the world.

One group that came together is called the Bangtan Nunna -- a Korean name which, loosely translated, means "mature fans of BTS." Nobody in the group is from Korea. Instead, the gathering of moms who all met online are from all over the country.

What's more, the Bangtan Nunna have children who adore BTS, but they consider themselves to be even bigger fans than their offspring.

"There's 14 of us, in the BTS party house" near MetLife Stadium, for the concert, said Jenny Keady, a Bangtan Nunna from New Hampshire. "So no kids allowed for this one."

At the pop up, there was no shortage of New Yorkers, either. Carmen Pastrana brought her 10 year-old daughter, Chailyn Diaz-Pastrana, from their home in the Bronx.

"I really like their stuff," Chailyn told PIX11 News. "They inspired me to learn Korean more."

Her inspired drive to learn the native language of the band that she loves so well was one of many reminders at the pop up that BTS is more than just a boy band.

"Their message of self love, being kind to each other, of appreciating each other," said ARMY Yvonne Cantwell, from Upstate New York, near the Canadian border. "That speaks to people of all ages," she said.

The devotion to the supergroup is remarkably real. Shopping in the pop up on Friday was Aileen White, a self-described "passionate fan" from Brooklyn. PIX11 News first encountered her camping out for days before BTS's Citi Field concert last October. She was also one of the first ARMYs sitting in line for days to get free tickets to the band's appearance on Saturday Night Live last month.

"There's this energy about the shows that's addicting," said White. "So that's why I'm so passionate about it."

She will be in attendance at both of the BTS concerts at MetLife Stadium, on Saturday and Sunday.

The shows begin at 7:30 p.m. each night. The parking lot at MetLife Stadium opens at 9:30 a.m.