When a South Korean monk performed a Buddhist ritual for a wildly popular K-pop boy band, it was the most unusual ceremony he had ever held.

His mission: to guide the souls of the band to peace and rebirth.

The band were long gone - or rather, they had never been alive, except in the fictional world of the animated Netflix hit K-pop Demon Hunters.

Still, the YouTube video went viral.

Although cast as villains, the Saja Boys have won a devoted following for their gorgeous looks and swagger. Even their name - saja - translates to angel of death, among other things.

The live-streamed service, a genuine Buddhist rite known as Chondojae usually performed by monks for grieving families, lasted more than two hours and drew more than 4,000 viewers - more people than he had ever seen for a ceremony, even offline, says the monk, a virtual YouTuber who prefers to remain anonymous.

This was no joke. The BBC confirmed that he is a registered monk. But he could not guarantee salvation for the Saja Boys, not even for the lead, Jinu.

That would depend on his good karma. I can guide him, but I can't promise.

As K-pop Demon Hunters tops every chart - Netflix says it has become its most-watched movie ever - Koreans are revelling in the moment. Made and voiced by Korean-Americans, and produced by US studios Sony and Netflix, the film's inspiration is deeply Korean.

It's a tale about mythical demon hunters whose power comes from their music - in this case, that's a sassy K-pop girl band called Huntrix. And of course, the soundtrack that fans across the world are now singing along to every day is rooted in South Korea's biggest export: K-pop.

All of this has sparked a frenzy in South Korea, like in so many other places, a fascination with the Korean culture the movie centers, and even a little bit of FOMO - because unlike in the US and Canada, there are no plans yet to release the movie in cinemas here.

Part of the fandom is driven by respect. Many Koreans are wary of clumsy depictions of their country on screen, especially given how popular the culture is right now. And to have such a global hit get it wrong would have stung.

I've seen plenty of films and dramas that touched on Korean culture, but they were always full of errors. They would confuse it with Chinese or Japanese traditions, show actors speaking awkward Korean, and reduce everything to a shallow imitation, says Lee Yu-min, a woman in her 30s.

But I was genuinely astonished at KDH's portrayal of our culture. Pointing to the opening scene, she says: A thatched-roof house from the Joseon Dynasty, ordinary people in hanbok [traditional Korean clothing] with their distinct hairstyles – the details were almost perfect.

The fandom in South Korea is no less. Surprisingly, one of the biggest beneficiaries has been the National Museum of Korea, which carries traditional Korean artifacts that are featured in the film.

Already the most visited museum in Asia, it now has queues stretching outside before the doors even open. It recorded more than 740,000 visitors in July, over twice as many as it had during the same time last year.

The soaring sales are a boost for people like Choi Nyun-hee, who runs the craft business Heemuse. My revenue has jumped about five-fold, she says, adding that her products are now being exported to the US and Australia.

Choi had previously worked at a museum, where she developed educational programs on Korean artifacts. After watching the film, she thought Korean culture was well-displayed and weaved together into a story.

More than two months after its release, the film's momentum hasn't slowed – in fact, it's spilling into cinemas. In North America, special sing-along screenings have made K-pop Demon Hunters Netflix's first number one film at the box office.

Now South Korean fans are clamouring for the same experience, with so many of them saying online and offline, I want to sing KDH in a cinema!!