It started small: a K-pop girl group that hunts demons. At first, critics called it a stretch—Sony Pictures and Netflix taking a gamble.

But the result? Monumental. Within a day of release, K-pop Demon Hunters topped charts in 22 countries, including the U.S., U.K., and Australia. By Day 3, it climbed to No. 1 in 31 countries; Day 4, in 41 countries.

With its animated visuals, addictive music, and a face-off between a demon-hunting girl group and a possessed boy group, it became a multi-sensory experience.

Who came up with this? Why a K-pop group? How did Ahn Hyo-seop get cast? What lyrics do TWICE love most?

Here are 10 behind-the-scenes facts about KDH.

(Warning: minor spoilers ahead.)

1. KDH was originally a low-budget project.

Director Maggie Kang initially conceived KDH as an indie animation. Early drafts painted a much darker tone—with more tragic characters and plotlines.

Everything changed when Sony Pictures came on board as producer and Netflix agreed to finance. Suddenly, KDH became a global-scale commercial animation.

Characters evolved too. Lumi was first written as a troubled family outcast. As the project scaled, her darker edges were softened to appeal to a broader audience.

2. K-pop wasn't the original concept.

KDH is the first animation to blend Korean occult mythology, K-pop, and action. It tells the story of exorcists disguised as K-pop idols battling ancient Korean demons.

But K-pop came last in the development process.

"I didn't set out to make a K-pop movie," Kang said. "My goal was to explore Korean demon folklore and mythology."

The K-pop idol concept was a narrative tool.

"Exorcists usually work in secret. I needed a disguise—and K-pop fit perfectly," she added.

3. Lumi was almost a solo artist.

In early drafts, Lumi debuted as a solo singer. But Sony Pictures questioned if one character alone could carry the emotional weight of the story.

Kang agreed. So two new characters—Mira and Joy—were introduced, transforming Lumi into the leader of a girl group. Thus, Huntress was born.

The team dynamic added depth. Instead of a solo journey, Lumi evolved through friendship, shared growth, and emotional bonds.

4. TWICE was the dream OST team.

From the beginning, TWICE was KDH's top pick for the soundtrack. Even while prepping their STRATEGY album, they gladly accepted the offer.

JYP selected members who matched the characters' energies: Jihyo, Jeongyeon, and Chaeyoung. They chose the track "Take Down" from the options provided.

Recording took place at JYP HQ, directed by Andrew Choi, who also voiced Jinwoo.

Their favorite lyric?
"Lose your mind, crush them, carve it in."

The mix of Korean and English was a hit with the group.

5. Ahn Hyo-seop is Jinwoo.

Casting Jinwoo took serious effort. Director Kang happened to be watching A Business Proposal and was struck by Ahn Hyo-seop's fluent English performance.

"I knew immediately he was the one."

They filmed Ahn during recording sessions to capture his facial expressions and gestures, later used to shape Jinwoo's idol visuals.

A love letter to Ahn is hidden throughout the film. In Jinwoo and Lumi's first scene, a K-drama cliché plays out—with Love, Maybe, the Business Proposal OST, suddenly playing.

6. Korea's first exorcists were girl groups.

KDH's strength lies in its cultural detail. It doesn't just use K-pop—it honors Korean music history by reimagining legendary girl groups as exorcists.

The flashback sequence drew praise for featuring the Jogori Sisters (1939), Korea's first girl group. The timeline then moves to the Kim Sisters (1953) and S.E.S. (1997).

Costumes, hairstyles, and props recreated each era with care. These tributes gave the story emotional depth and cultural grounding.

7. Is Mystery… not human?

Rumors swirled about Mystery, the member of Lion Boys. His hair hides his face, and his primal instincts sometimes surface unexpectedly.

Pay close attention to his transformation scene. Mystery shows long fangs as he shifts into human form. At a fan sign event, he even growls at fans.

Some fans believe he's a Sapsal dog, a traditional Korean spirit-chasing breed. In folklore, they're also called "lion cubs." One theory? Mystery was possessed while hunting ghosts.

8. Lotte Tower, are you watching?

Set in Seoul, KDH features many real locations—like Naksan Park, Bukchon Hanok Village, and Gangnam Station. But the standout backdrop is Namsan Seoul Tower.

Art Director Celine Kim obtained full licensing rights and recreated the landmark with near-perfect detail.

"Getting approval from Namsan Tower was a miracle," she joked online. "Made my life 100x easier. Are you watching this, Lotte Tower?"

9. Archery at the Idol Games? Almost.

A scrapped concept? The Idol Star Athletics Championships (ISAC). Early versions had Lumi and Jinwoo competing in archery.

But executives vetoed the idea.

"The team asked, 'Why are they suddenly doing hurdles and archery?'" Kang told Forbes.

Instead, the scene was rewritten as a joint fan signing event between the girl and boy groups—ironically, a more far-fetched concept for many K-pop fans.

10. Jinwoo's eyes held the truth.

From their first meeting, Jinwoo clashed with Lumi. Exorcist vs. possessed. But slowly, their emotions began to intertwine.

The film's climax sees Lumi in a final showdown with the demon. Jinwoo, torn between two worlds, ultimately sacrifices himself to save her.

Look closely at his final moment. Even in monstrous form, his human eyes remain. The camera lingers on them—revealing that his soul never fully turned.