Jeon So-nee. That's the name you're probably googling right now after finishing that wild grocery store scene. Honestly, the way she manages to toggle between the dead-eyed stare of a parasitic lifeform and the fragile, broken spirit of Su-in is the only reason the show works. If the Parasyte: The Grey cast hadn't been anchored by actors who could sell the "uncanny valley" look, the whole thing would have collapsed into a heap of goofy CGI.
Director Yeon Sang-ho—the guy who gave us Train to Busan—didn't just remake the original manga. He shifted the setting to South Korea and built a brand-new story. This meant the casting had to be perfect to convince fans of Hitoshi Iwaaki’s legendary source material that this spin-off was worth their time. It's not just about the monsters. It's about the people trying to survive them.
Jeon So-nee as the reluctant host Su-in
Jeon So-nee plays Jeong Su-in. She's a cashier at a retail mart whose life is already pretty miserable before an alien larva tries to eat her brain. It fails. Sorta. Because Su-in’s body was dying from a literal stabbing during the invasion, the parasite—later named Heidi—had to use its energy to heal her wounds instead of fully taking over her mind.
This creates a "mutant" situation where they share a body but can't communicate in real-time. Jeon has talked in interviews about how difficult it was to act against nothing, basically flailing her head around so the VFX teams could add the tentacles later. She had to develop two distinct physical languages. As Su-in, she's hunched, quiet, and perpetually exhausted. As Heidi, her posture straightens, her voice drops an octave, and she loses all human rhythm. It’s unsettling.
Jeon wasn't an obvious choice for an action-heavy sci-fi lead. Most people knew her from Our Blooming Youth or Soulmate. But that's why it works; she has this inherent "everyman" quality that makes the body horror feel more grounded and less like a superhero movie.
Koo Kyo-hwan brings the chaos
If you’ve seen D.P. or Kill Boksoon, you know Koo Kyo-hwan is a scene-stealer. He plays Seol Kang-woo, a small-time gangster who is searching for his missing sister. He ends up becoming the bridge between Su-in and her parasite.
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Koo is weird. In a good way. He brings a frantic, twitchy energy to the Parasyte: The Grey cast that balances out the stoic nature of the parasites. He’s essentially the audience surrogate, reacting to the madness with the exact level of "what the hell is happening" that we all feel. Kang-woo is a loser, basically. But he’s a loser with a heart, and his chemistry with Su-in—which is platonic and protective—is the emotional spine of the series.
Interestingly, Koo Kyo-hwan and Director Yeon Sang-ho have a history. They worked together on Peninsula, the sequel to Train to Busan. Yeon clearly trusts Koo to improvise and add those tiny, human tics that make a character feel real rather than just a script device.
The intensity of Lee Jung-hyun as Choi Jun-kyung
Then we have Lee Jung-hyun. She plays Choi Jun-kyung, the leader of "Team Grey," the specialized task force hunting these things. Her character is controversial among fans. Some find her performance over-the-top, while others think it perfectly captures a woman who has literally lost her mind to grief and obsession.
Choi Jun-kyung uses the mutated head of her own husband—who was turned into a parasite—as a "radar" to find others. It’s dark. It’s grisly. Lee Jung-hyun plays this role with a frantic, almost manic intensity. She’s not your typical cool-headed commander. She’s vibrating with rage.
Lee is actually a legendary figure in Korean entertainment. She was a massive K-pop star in the late 90s (known as the "Techno Queen") before becoming a powerhouse actress. To see her trade the glitz of her music career for a tactical vest and a shotgun is quite the pivot. She actually filmed this shortly after giving birth, which is wild considering the physical demands of the role.
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Supporting players and the "Church" of parasites
The villains in this show aren't just mindless monsters; they’re organized. Kim In-kwon plays Kang Won-seok, a detective who... well, let’s just say he has complicated loyalties. Kim is usually known for comedic roles, so seeing him play someone so cynical and duplicitous is a refreshing change of pace.
The "Grey" task force also includes Kwon Hae-hyo as Cheol-min, the veteran detective who acts as a father figure to Su-in. Kwon is one of those "I’ve seen that guy in everything" actors. His presence brings a much-needed warmth to a show that is otherwise very cold and clinical. He represents the old-school morality that is being threatened by this new, cold-blooded biological evolution.
The Cameo that broke the internet
We have to talk about the ending. If you haven't seen it, stop reading. Seriously.
In the final moments of the series, a man introduces himself to the Team Grey headquarters as Shinichi Izumi. He is played by Japanese actor Masaki Suda. For fans of the original Parasyte manga and anime, this was a massive "Avengers-level" moment. Masaki Suda is a huge star in Japan (CUBE, Character), and his appearance confirms that the Korean series exists in the same universe as the original Japanese story.
His right hand is hidden. We know why.
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Why the acting matters more than the CGI
You can have the best digital effects in the world, but if the actors don't sell the physical pain of their heads splitting open, it looks cheap. The Parasyte: The Grey cast had the unique challenge of "acting toward the future." They had to react to things that weren't there, maintaining a sense of horror while often wearing green-screen hoods or motion-capture markers.
The series explores the idea of "The Organization." Humans have them—police, gangs, churches—and the parasites realize they need them too. This social commentary only lands because the actors play the "human" versions of the parasites with a chilling lack of empathy. They look like us, but they don't feel like us.
How to dive deeper into the Parasyte universe
If the Netflix show was your first introduction to this world, you're actually missing out on a lot of context. The show is great, but it's a slice of a much larger pie.
- Watch the 2014 Anime: Parasyte: The Maxim is widely considered a masterpiece. It follows Shinichi and Migi (the parasite in his hand). It’s more philosophical and focuses heavily on the question of what defines a "human."
- Read the Manga: Hitoshi Iwaaki’s original work from the late 80s/early 90s is the foundation. The art is dated, but the pacing is incredible.
- Track the Cast’s Other Work: If you liked Jeon So-nee, check out Soulmate. It couldn't be more different from The Grey, showing her range as a dramatic actress. If you want more of Koo Kyo-hwan’s weirdness, D.P. on Netflix is mandatory viewing.
The best way to appreciate the performances in The Grey is to see where these actors came from. They aren't "action stars." They are character actors who were thrown into a high-concept body horror nightmare and decided to give it 100%. That's why people are still talking about it.
Start by re-watching the first episode and paying attention to Su-in's eyes during the grocery store confrontation. The subtle shift from fear to total emptiness is a masterclass in physical acting. Once you see it, you can't unsee the level of detail the cast brought to this adaptation.