K-pop group Brave Girls performing during a rehearsal for a Youtube-livestreamed commercial event.

The Brave Girls were losing courage just weeks ago, on the verge of breaking up and abandoning their dreams of K-pop stardom after years of going nowhere.

Then a pseudonymous YouTuber called Viditor uploaded a compilation of them performing on South Korean army bases -- and saved their careers.

"Rollin' rollin' rollin' rollin'/I am waiting for you/Babe just only you," they chant, as wildly enthusiastic uniformed conscripts dance and wave glow-sticks.

It went viral and struck millions of chords across the country.

Less than a month later the song reached number one in South Korea and topped the Billboard K-pop 100 in the US, four years after it was originally released -- with their popularity reinforced by their story of struggle against the odds.

The fan-led ascent is a reversal of the usual K-pop model, where bands are usually assembled, trained intensively and launched by record companies, whose marketing and promotion is crucial to their success.

The Brave Girls started out as a five-piece a decade ago, but fell largely on deaf ears. They were relaunched as a septet in 2016, but the reshuffle did nothing to boost their popularity.

 One of their songs reached number one in South Korea and topped the Billboard K-pop 100 in the US.

'We will definitely win wars'

South Korea requires all able-bodied men to serve in uniform to defend it against the nuclear-armed North, a period when they are often dispatched to remote places and deprived of the joys of modern life.

As a common experience it is a unifier and a leveller, and Viditor's compilation -- complete with witty captions such as "Play this song during battles and we will definitely win wars" -- resonated with those who had seen them in the military.

The clip garnered around 15 million views in little more than a month.

The uploader -- who said she wanted to remain anonymous to maintain her privacy -- said she had been astonished by the reaction.

She has put together hundreds of compilations of other bands' tracks but never before had similar impact.

'Something miraculous happened to us'

The K-pop phenomenon -- epitomised by the global success of BTS -- earns billions of dollars a year for the world's 12th-largest economy.

Scores of groups largely made up of teenagers are launched every year hoping to follow in their footsteps, but most acts quickly disappear, leaving barely a trace on the score of musical history.

Exposure on major television stations has long been a must-have for aspiring K-pop idols. But cultural commentator Jung Ho-jai said the raunchy moves in the original "Rollin'" video were too risque for the networks.

K-pop firms are increasingly turning to social media sites like YouTube, TikTok and Facebook to develop their bands' fanbases.

But for the Brave Girls, it was an amateur poster who made the difference.

Member Lee Yu-na said: "Something very miraculous and inexplicable has happened to us."