Ear-splitting screams burst out the instant the iconic opening beats of "Again and Again" raised the curtains on boy band 2PM's concert in Seoul on Sunday. Blue laser beams flashed to the beat of the song that turned into a heart-pounding medley of the band's greatest hits.

Even those who are not fervent fans of 2PM would recognize every part of the medley, as it thread through songs that had reigned the local music charts in the late 2000s to early 2010s.

Sunday's gig at Jamsil Arena marked the second night of the veteran K-pop band's 15th anniversary concert series, "It's 2PM." It was the six-member group's first live music event in six years.

It was a walk down the memory lane from the start as the night opened with the group's 2011 hit, "I'll Be Back," followed by "Jump" from 2015 and "Go Crazy!" from 2014, the last of which made fans shoot to their feet. At "Hands Up," from 2011, the jam-packed audience erupted into feverish cheers.

The six men -- Jun. K, Junho, Nickhun, Taecyeon, Woo-young and Chan-sung -- gathered center stage to greet the crowd in different languages, from Chinese to Japanese and Spanish.

"We're seeing you guys for the first time since we held '6Nights' in 2017. It's been so long," Woo-young said, referring to the band's last concert.

Taecyeon, his face brimming with a cheeky grin, said, "It's the second night of our 15th anniversary gig, and it's even hotter than yesterday. I love it."

A highlight of the night was "Must," which was performed onstage for the first time after it came out in 2021. It marked the miraculous reunion of the members, now affiliated to different companies, who had been on hiatus because of their mandatory military service.

Much of the night was a major throwback to 2PM's glory days, as the six members shared past stories, big and small, that unfolded along their music career.

"When we made 'Must,' all we thought were things like, 'We must get back to our fans' and 'We must release a new album.' Those desires were naturally reflected in the album, and it came to be titled 'Must,'" Woo-young said.

The nearly three-hour concert was a culmination of 2PM's everything and essence, as put by the members that night. The group brought to the stage some of its biggest hits, such as "Comeback When You Hear This Song," "I Can't," "10 Out of 10," as well as hidden side-track gems, "Shall We?" and "Magic."

After an outfit change into sleek suits, the group blasted into a breathless relay of the band's fan-favorites that began with "My House" and ran into "Promise" and "A.D.T.O.Y." At "I'm Your Man," another career-defining song from 2014, the six men snatched off the ties from their necks, while some ripped open their shirts, sending fans into a screaming frenzy.

Thousands of fans packed the seats at the stadium that night, from longtime grownup fans who've supported the boy band since their debut in 2008 to newcomers, some born when the group debuted. Among the crowd was the band's creator and executive producer of JYP Entertainment, J.Y. Park -- aka the Asian Soul -- who was captured on screen waving at the members.

Perhaps a feat that can only be pulled off by a veteran group in its 15th year, the bandmates took turns performing solo songs spontaneously at the request of fans. Jun. K belted out his 2014 solo song "No Love," which the singer said he sang for the first time since 2017, while Woo-young dropped rusty hip-hop beats to his 2018 song "I Like," and Chan-sung cooed out "Perfume" over what sounded like a karaoke version of the song.

The mood then turned mellow with ballads "At Times," "One More Day" and "OK or Not," with fans singing gently along.

The concert's emotional crescendo culminated in the next part as the band pulled out all the stops for "Again & Again," "Without U" and "Heartbeat," songs that laid the foundation of the sextet's ferocious, performance-strong music.

After putting out "I Hate You," "Game Over" and "Don't Stop Can't Stop," the bandmates began its encore section with "Thank You." They then blew candles off a cake on the stage and took a moment to deliver heartfelt messages to fans.

"It was a dream-come-true moment for us tonight. It was an indefinite wait and tonight I'm finally relieved from the stress all thanks to you guys," Woo-young said, adding, "2PM will continue, and the reason is you guys that came here tonight. Tonight will be the reason why 2PM could continue."

"So much has happened in the past six years, and I feel it a huge blessing that we could stand on the stage again together," Taecyeon said, to which Nickhun piped in, saying, "As long as you guys wait for us, we will continue."

Junho said he will never forget the sound of the fans' cheers as they waited below stage.

"Fifteen years is no easy time to last, and I realized that our songs had reached you guys and you've kept them inside you until now," he said.

Jun. K described his fellow members as "the biggest luck" in his life, and extended his gratitude to everyone who had helped them continue.

Chan-sung said to the fans: "The biggest joy in holding the concert is seeing your eyes brimming with love. Thank you."

2PM rounded out the night with "Hold You," "Zero Point," "Goodbye Trip" and "Hot."

"It's 2PM" is set to continue in Tokyo, Japan, on Oct. 7-8.