The excitement on the tour bus was palpable. From young kids to grandmothers, the Australians had come to Seoul with one aim: to celebrate 10 years of their favourite K-pop band BTS.

Wearing novelty headbands and hats in the supergroup's official colour, purple, and brandishing huge cut-outs of their favourite members' faces, the fans -- from the Australian chapter of BTS's global following, known as ARMY -- burst into song.

"Happy birthday to you, happy birthday to you, BTS!" the 28 people on the bus sang in unison, before segueing into enthusiastic covers of BTS's many hits, complete with lip-syncing and dance moves.

The fans are on a 12-day "BTS tour" of South Korea to mark the 10th anniversary on Tuesday of the group's debut. Organised in part by Seoul's official tourism board, their trip takes in a range of locations nationwide associated with the K-pop juggernaut.

First up on Tuesday: the main Seoul office of the group's agency HYBE, which has become a pilgrimage site for fans this week, and where a huge mural of the septet has been freshly painted on the wall outside.

"I am just happy that we are here right now, the Australian ARMY tour group... It's such a milestone to be here while the boys are celebrating their 10th year," Barbara Pena, a 48-year-old real estate agent from Sydney, told AFP in front of the mural.

Pena, the admin of the BTS Australia fan group, has been to South Korea four times previously, with each trip themed around BTS.

She estimated this trip cost participants around $5,000 per person, including flights.

It was worth it, she said, because BTS "changed my life".

Discovering BTS had helped her realise she "could do so much more", including travel places she never imagined she would go, Pena said, rattling off destinations she had visited to see the band. 

"And now I have so many of these memories and experiences I can share with my grandchildren," she added.

- 'Struck a chord' -

On June 13, 2013 a seven-member hip-hop group put together by one of South Korea's smaller music labels debuted under the moniker Bangtan Sonyeondan -- or "bulletproof boy scouts".

The initial domestic reception was muted. Their name was seen as strange, and in South Korea's highly competitive music market, being repped by a smaller label meant they were squeezed out of the mainstream, forcing them to find fresh ways to connect with fans.

Gradually, as they broadened their musical style and increasingly went by the snappier name BTS, their albums started to rise up local and global charts. By 2018, their third album -- "Love Yourself: Tear" -- went straight to the top of the Billboard 200, prompting congratulations from the South Korean president at the time.

Their direct outreach to fans online, coupled with their heartfelt music, has won them legions of adorers like Pena, whose eyes well with tears when she thinks of the song that means the most to her: "Love Myself".

"There's a part that says, 'Why is it so hard for you to love yourself and easy for you to love other people?' and that struck a chord," she said.

Although the band is currently on a hiatus, with two members performing their mandatory military service, they released a new digital single last week and have thrown themselves into celebrating the anniversary.

– Family bonding –

Pena's tour, meanwhile, has already ventured far afield -- the Australians did six hours round trip on their bus to the eastern city of Gangneung to see a bus stop where BTS once posed for an album cover.

They have also visited a Korean barbeque restaurant that BTS eat at, and a cafe run by band member Jimin's father.

For Darrin Goodwin, 52, this was the undisputed highlight of the tour -- especially as Jimin's father gave him an unexpected hug after their chat. 

"It was very very surreal and it was an honour and privilege," Goodwin said. 

Goodwin told AFP that he was not originally a BTS fan, but his daughter Chelsea had got him into the band. 

"I tried to convince my dad to listen to them but it didn't work until he heard a specific song, 'Dope'," she told AFP.

Now, the father-daughter duo say they do everything BTS-related together, and credit their shared love of the band with bringing them closer as a family.

For Chelsea, 24, BTS is more than a K-pop group. They have made the world a happier place, she said, by teaching people "how to love themselves".

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