When Netflix first announced the Gyeongseong Creature season 1 cast, people basically lost their minds. You had Park Seo-joon and Han So-hee—two of the biggest Hallyu stars on the planet—teaming up for a gritty, historical horror. It felt like a fever dream for K-drama fans. But honestly? The show ended up being way more than just a vehicle for its lead stars.
Set in the spring of 1945, right at the tail end of the Japanese occupation of Korea, the series is heavy. It's dark. It's kinda gross at times (thanks to the biological experiments). What really kept the whole thing grounded, though, wasn't just the CGI monsters, but the humans fighting them.
The Power Duo: Park Seo-joon and Han So-hee
Let's talk about the big names first.
Park Seo-joon plays Jang Tae-sang. If you’ve seen him in Itaewon Class or What’s Wrong with Secretary Kim, you know he’s got range. Here, he starts off as this flashy, incredibly wealthy owner of the House of Golden Treasure (Geumokdang). He’s the guy who knows everyone and has everything. But beneath the fancy suits, Tae-sang is a survivalist. His mother’s final words to him were literally just to stay alive, and he took that to heart by becoming the most pragmatic man in Gyeongseong.
Then you have Han So-hee as Yoon Chae-ok. She’s a "Todugun"—a specialist in finding missing people. She’s tough. Like, really tough. She spent her youth wandering Manchuria and Shanghai with her father, learning how to use knives and firearms. Han So-hee basically ditched the glamorous vibes of her previous roles to get covered in dirt and blood for this one.
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Their chemistry isn't your typical "love at first sight" K-drama trope. It’s a slow, painful burn born out of mutual desperation.
The Villains and the Victims
A show like this is only as good as its antagonists.
Claudia Kim (you might recognize her as Nagini from Fantastic Beasts) plays Lady Yukiko Maeda. She is terrifying. Not because she screams or fights, but because she’s so calm. She’s the secret benefactor behind Onseong Hospital, where the experiments happen. While her husband, Commissioner Ishikawa (Kim Do-hyun), is out being the public face of the occupation, Maeda is the one pulling the strings.
Then there’s the medical nightmare team:
- Choi Young-joon as Lieutenant Colonel Kato: The "mad scientist" vibe is strong here. He’s the one obsessed with the Najin parasite.
- Hyun Bong-sik as Ichiro: The director of the hospital who’s just trying to stay in the military’s good graces.
And we can't forget Kang Mal-geum, who plays Choi Seong-sim. She’s Chae-ok’s mother, but viewers mostly see her as the "Creature" itself. It’s heartbreaking because the director, Chung Dong-yoon, actually focused on making the creature look sorrowful rather than just scary. Those swollen eyes? Those were intentional to remind you there was once a mother inside that monster.
The Supporting Cast That Stole the Show
If you’ve watched enough K-dramas, the supporting Gyeongseong Creature season 1 cast will feel like a reunion of your favorite veteran actors.
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Kim Hae-sook plays Mrs. Nawol (Nawol-daek). She’s the moral compass of the Geumokdang pawnshop. She’s been looking after Tae-sang since he was a kid, and her loyalty is honestly one of the few wholesome things in this show. Alongside her is Park Ji-hwan as Gu Gap-pyeong, the butler. He provides a bit of much-needed levity in an otherwise depressing setting.
Wi Ha-joon (the cop from Squid Game) plays Kwon Jun-taek. He’s Tae-sang’s best friend but lives a double life as an independence activist. His arc is actually pretty controversial among fans because he cracks under torture. It’s a very human moment—he’s not a superhero; he’s just a guy trying to do the right thing and failing.
Jo Han-chul plays Yoon Joong-won, Chae-ok’s father. He’s spent ten years looking for his wife, and his desperation is the catalyst for the entire plot.
Why the Casting Was Controversial (and Brave)
Here’s something most people don't realize: playing these roles was a huge risk.
The director mentioned in interviews that many actors were hesitant to join projects set during the Japanese colonial era for nearly a decade. Why? Because the "Korean Wave" is massive in Japan. There’s a fear that taking on a role in a show that depicts Japanese military atrocities might hurt an actor's popularity or career in Japan.
Park Seo-joon and Han So-hee taking these roles was seen as an act of courage. They chose the story over potential brand deals or marketability. That adds a layer of weight to their performances that you don't see in every drama.
Breaking Down the "Najin" Mystery
While the actors did the heavy lifting, the "Najin" parasite was basically a cast member of its own. It’s what turns humans into monsters. In the show, the Japanese military uses it to create a biological weapon.
The most pivotal moment for the cast happens at the end of Part 1. A glass of water contaminated with a parasite is left out. We see the glass is empty, but we don't know who drank it. Was it Tae-sang? Chae-ok? Someone else? That cliffhanger worked so well because we were already so invested in these specific characters.
Actionable Takeaways for Fans
If you're just finishing Season 1 or looking to rewatch it, keep an eye on these specific details:
- Watch the eyes: Pay attention to the "Creature’s" eyes in the later episodes; they reflect the mother’s grief.
- Background Details: Look at the "House of Golden Treasure" set. The actors noted how immersive it was, and the art direction is packed with 1940s-era easter eggs.
- The Soundtrack: Listen to how the music changes when Maeda enters a room versus when Chae-ok is on screen. It tells you everything about their power dynamic.
For those moving on to Season 2, remember that the "cast" shifts quite a bit as the story jumps to modern-day Seoul. But the echoes of these Season 1 characters are everywhere.
To truly appreciate the performances, you should check out the "Behind the Scenes" interviews on Netflix K-Content’s YouTube channel. You'll see Park Seo-joon and Han So-hee joking around, which is a wild contrast to the miserable, life-or-death stakes they’re dealing with in the actual episodes.
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The best way to experience this cast's work is to watch the show in its original Korean audio with subtitles. The nuances in how they switch between Korean and Japanese (depending on who they are talking to) add a layer of tension that dubbing just can't capture.