BTS star Jin starts his mandatory South Korean military duty on Tuesday, the band’s first member to enlist since a hiatus announcement this year left fans heartbroken over the K-pop juggernaut’s uncertain future.

The septet is widely considered the country’s biggest-ever cultural phenomenon — selling out stadiums around the world and dominating the charts while raking in billions and building a global legion of fans known as ARMYs.

But all able-bodied men in South Korea must serve at least 18 months in the military, and while there was a years-long debate about whether BTS deserved an exemption, they confirmed in October that all members will enlist.

Jin — whose full name is Kim Seok-jin — will begin five weeks of training on Tuesday, the military said.

Yonhap news agency reported the star is expected to be deployed to a “frontline” unit near the border with North Korea, with which South Korea remains technically at war.

“We ask you to keep your heart-warming words of support and farewell in your hearts,” BTS’s label Big Hit Music told fans last week, urging them to stay away from the families-only entrance ceremony.

Fans were stunned in June when the group revealed that it was going on hiatus, citing exhaustion and pressure as well as the desire to pursue solo careers.

But analysts said the announcement was strategically timed because of the compulsory military duty.

The group will reunite around 2025, when its seven members have completed their service.

“For a while, it’s true that there were many fans who would spend days just crying,” a South Korean fan, who runs the Twitter account @5heterotopia, told AFP.

Nimah Mustafa, a 20-year-old fan in Dubai, added: “(Jin’s absence) will be like a huge… void for me.”

South Korea exempts some elite athletes, such as Olympic medallists, and classical musicians from duty, but pop stars do not qualify.

However, BTS have already benefited from a 2020 revision to the conscription law that raised the enlistment deadline for some entertainers from age 28 to 30.

Jin, the oldest member of BTS, turned 30 on December 4.

– ‘They won’t be forgotten’ –

The seismic changes for BTS in 2022 have sparked feverish speculation among fans and K-pop watchers about what the future holds for the group — will they retain their fame or struggle to revive that success?

Some male K-pop stars have struggled to resume their careers after military service in a cut-throat industry where artists are easily replaceable.

“For the K-pop industry, the retreat of BTS will be a big deal,” Lee Taek-gwang, a communications professor at Kyung Hee University, told AFP.

“During the absence, they could lose public interest, and the decline in popularity will damage their business. It would not be easy for the boy band to reunite.”

However, other experts have pointed to the massive success of BTS and said they will be an exception to that trend.

They “obtained another level of popularity, influence and credibility”, said Lee Ji-young, a BTS expert and professor at Hankuk University of Foreign Studies.

“So they won’t be forgotten by other artists in a highly competitive K-pop industry,” she told AFP.

Since their debut in 2013, BTS have been widely credited with doing more than any diplomat or other celebrity to boost the image and soft power of South Korea, today considered a global cultural powerhouse.

They have been invited to speak at the United Nations, and to meet US President Joe Biden at the White House. They are also official ambassadors to bring the 2030 World Expo to Busan, South Korea.

The South Korean government has credited BTS with bringing billions of dollars into the economy.

– ‘Frontline’ deployment? –

But despite that success, a draft proposal to grant them service exemptions proved too controversial and never made it through parliament.

“In South Korea, the military service is the indicator of egalitarianism… (where) all men are equal,” Lee at Kyung Hee University told AFP, adding that it was a “necessary” symbol of citizenship.

Jin will reportedly join a “frontline” unit stationed near the border with North Korea.

“It shows the role of culture, and public opinion, in shaping international affairs. Is this ‘frontline’ role a combat role, or is it about public relations and media?” Sarah Keith, a senior lecturer in media and music at Macquarie University, told AFP.

Jin bid farewell to thousands of tearful fans in Buenos Aires in October when he performed his new song “The Astronaut” with Coldplay.

On Monday, he posted a photo of himself with military-style cropped hair on the South Korean social media platform Weverse, with the caption: “It’s cuter than I expected.”