PUBLISHED ONMarch 12, 2025 10:07 AMBySyarifah NadhirahIf South Korean actor Seo Kang-joon had to list down the hardest days of his life, the one which he spent filming a particular action scene from his new drama Undercover High School would make it to the top three.
The 31-year-old recalled the experience in a recent interview with AsiaOne for the ongoing series where he stars as Jung Hae-sung, a National Intelligence Service (NIS) agent who goes undercover as a high school student for a special mission.
"It was extremely tough filming the action scene (in episode four) in the scorching heat. Even though I was prepared for it, the heat got to me and I remember struggling a lot. If I had to pick the hardest days of my life, this one would probably make it into the top three," said Kang-joon.
In the above-mentioned scene, Hae-sung, in his school uniform, goes up against five to seven bad guys on his own in a dingy warehouse, and Kang-joon said those were his toughest stunts in the entire drama.
"Not only did I have to fight multiple opponents, it was also physically exhausting."
Co-star Jin Ki-joo plays Hae-sung's homeroom teacher Oh Su-a, who notices the similarities between Hae-sung and her childhood first love who had left her heartbroken and filled with painful memories.
She told AsiaOne besides performing action scenes in a dress, she also had to learn how to play the piano.
"There was a scene where I had to play the school anthem, but since I didn't know how to play the piano, I spent a lot of time practicing. On the first day of practice, I was so immersed that I ended up playing for seven hours straight," said the 36-year-old.
Undercover High School is Kang-joon's first drama after getting discharged from the military in 2023, so we asked if it was difficult getting back into the swing of things on set.
"We had to run 3km every morning in the military, which I think really helped improve my stamina. Plus, since there wasn't much to do during break times besides working out, I ended up exercising a lot, which turned out to be beneficial," he recalled.
"Since it had been a while since I last acted, I tried to recall as much as I could and studied hard. Fortunately, I hadn't forgotten as much as I thought I would."
He added that his free time during his enlistment also helped him "stay connected to acting".
When asked how similar Hae-sung is to himself in real life, Kang-joon said they share a similar perspective on the world.
"When looking at something, neither of us sees it as purely beautiful nor entirely negative. If something is beautiful, I tend to believe there must also be flaws within it, and if something seems negative, I believe there must still be good or redeeming aspects.
"Hae-sung seems to think the same way - both the light and dark sides of the world co-exist, and together, they form its true nature."
Meanwhile, Ki-joo feels she doesn't have many similarities to her character.
"Su-a is outgoing, whereas I'm more introverted, which I think is a major difference between us," she said.
Undercover High School is streaming on Viu, with new episodes released every Saturday and Sunday.
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