How Two Songwriters From K-Pop and Musical Theater Built This Summer’s Surprise Chart Smash

When songwriters Mark Sonnenblick and EJAE were first contacted to work on Netflix’s ambitious animated musical KPop Demon Hunters, the two thought it would be a fun and unique project to add to their musical résumés. A madcap animated film following a K-pop girl group who moonlight as the mystical destroyers of an invisible demon realm — what’s bolder than that? 

But now, five weeks after KPop Demon Hunters’ Netflix premiere, the film has skyrocketed to take the title of the streaming platform’s most-watched animated film ever. As for the music, it’s surpassed everyone’s expectations, peaking at Number Two on the Billboard 200 albums chart and becoming the highest-debuting soundtrack of the year. And how are EJAE and Sonnenblick feeling about this surprise success? Absolutely golden. 

“It’s crazy! Unbelievable,” EJAE tells Rolling Stone over Zoom from her home studio in New York. 

“Has any songwriter been like, ‘It’s charting? What a disaster!’” Sonnenblick adds, laughing. “We loved the songs and believed in the music. It’s just a testament to the hundreds of people who worked on this film. The film supports the music. The music supports the film. It’s amazing.” 

In the past decade-plus, K-Pop has grown into a global phenomenon and a multi-billion-dollar industry, driven by incredibly devoted fanbases and the constant introduction of new groups to drive up interest. Against this backdrop, directors Maggie Kang and Chris Appelhans introduce audiences to fictional singers Rumi, Zoey, and Mira — or, as their hordes of screaming fans know them, superstar girl group HUNTR/X. What those fans don’t know is that when HUNTR/X  hit the stage with their synchronized struts, sharp harmonies, and killer outfits, their music is really strengthening the Honmoon, a magical barrier that protects humans from the hungry, soul-sucking demons on the other side. Everything is going according to plan, until rival group the Saja Boys reveal their true purpose: They’re demons on a mission to steal HUNTR/X’s fans and their souls.  

That mystical battle is buoyed by a 12-song soundtrack built by some of the biggest names in K-pop production, including THEBLACKLABEL, co-founded by Teddy Park. But while fans continue to be obsessed with HUNTR/X — the fictional group has even outpaced Spotify records set by real-life superstars BTS and Blackpink — Sonnenblick and EJAE tell Rolling Stone that writing their songs wasn’t as easy as hitting the right notes. It required each of them to learn a new musical language. 

“I was pretty new to K-pop,” says Sonnenblick, who’s better known for his work as a composer and writer for musicals including the 2022 film Spirited and the stage version of The Devil Wears Prada. “I knew some of the baseline stuff that had broken out in America. But I’d never heard NewJeans. That’s what’s exciting about entering into new collaborations with new genres. The music is so expansive and theatrical — the minute I heard it, it’s like ‘This is music to kill demons to.’”

EJAE, by contrast, has lots of experience with K-pop. Born in Seoul, she’s spent her career immersed in that world, writing with groups like TWICE, Aespa, Le Sserafim, and Red Velvet. Much of her learning curve involved staying true to the genre’s musical maximalism while also keeping the storyline front of mind in a way she’d rarely had to before. 

“We both have partners, but Mark was like my other partner, my writing boyfriend,” EJAE jokes. “We had the best collaboration, because Mark’s from theater and I’m from K-pop and pop writing, so we were both kind of each other’s police. Like, ‘No, no, EJAE — back to the storyline,’ and then I’d go, ‘No, no. Mark, I don’t like that lyric. Let’s make it more in the pop world.’”

In addition to her role in writing several of the KPop Demon Hunters songs, including “Your Idol,” “Golden,” and “How It’s Done,” EJAE was also the on-screen singing voice of Rumi, a role where she found herself drawing on her history in the K-pop world. K-pop groups are typically built by labels and management groups, who sign potential stars to contracts and then take them through a rigorous vocal and dance training program to see if they can fit in any new groups. The idol hopefuls are called trainees, and for almost 10 years, EJAE was one of them, working with SM Entertainment, one of the biggest companies in the industry.

“I got in when I was 11,” she says. “I feel like I experienced all facets of K-pop. I was a trainee, I became a songwriter, I also vocal directed for K-pop idols.  So I really resonated with Rumi. She’s such a perfectionist and trying to hide her shame, hide her flaws. And  that’s a huge part of when you’re training. You’re trying to put your best foot forward. ‘Golden’ really means a lot to me, because I feel like at that time, I needed a song like that.” 

“I’m done hidin’, now I’m shinin’/Like I’m born to be/We dreamin’ hard, we came so far/Now I believe,” the lyrics declare, building to a frenetic harmony as she belts out the chorus that’s become a staple everywhere from grocery store aisles to EDM festivals: “We’re goin’ up, up, up/It’s our moment/You know together we’re glowin’/Gonna be, gonna be golden.”

Both of the songwriters credit the strength of their collaboration to the vision of the film’s directors and executive music producer Ian Eisendrath, which allows all of the songs to do double duty as bangers on the charts and also necessary narrative devices onscreen. “The main goal was, is this a song that can actually compete with other K-pop idols?” EJAE says. “Can it fit in?”

Sonnenblick adds that he feels the songs can stand on their own outside the film. “You go and watch the movie and ‘Golden’ is this kind of misguided thing that they have in the beginning so that they can break open and find their real voice at the end,” he says. “But you’d never know that from listening to this on its own.”  

“Golden” has become the biggest hit from the soundtrack, with Netflix confirming that they plan to submit it for consideration in the Best Original Song category at the 98th Academy Awards. It’s a major win for Sonnenblick and EJAE, considering the two spent nearly five years and countless hours perfecting the songs that are now dominating playlists. “It’s 3 a.m., we’re almost in tears, my God, on our fifteenth round of notes or whatever,” Sonnenblick recalls. “But we were like, ‘If we pull this off, it could be huge.’” 

For EJAE, the success of “Golden” reflects a more personal breakthrough, something that she feels makes the film’s connection to Korean culture even stronger. 

“The thing about Korean culture I’ve noticed is that we try not to burden other people with our issues. That’s a big part of the culture,” she says. “But I love how the movie really tries to say, ‘When you need help you can’t do it alone. Do it with people who you love. Ask for help.’” 

She takes a deep breath before continuing: “I don’t know if Mark knows this, but when I wrote ‘Golden,’ I was going through a hard time. I actually cried singing the demo, because it resonated with me so much. Maybe that’s why ‘Golden’ is ‘going up up up.’ Because everyone’s going through a hard time.  And they want to feel hope.”