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Netflix premiered the South Korean action thriller Mantis on Friday, September 26, 2025, at 4 pm KST. The film is director Lee Tae-sung's feature debut for the platform and is co-written with screenwriter Byun Sung-hyun. Headlined by Im Si-wan and Park Gyu-young, Mantis expands the universe of the 2023 hit Kill Boksoon, serving as its official spin-off
The story is about Mantis, a top assassin, who returns from vacation to find the underworld in turmoil. Facing his old rival Jae-yi and retired legend Dok-ko, he's pulled into a deadly fight for dominance.
The film lacks in storytelling greatly. It's weak plot make it less engaging as a standalone film. For most viewers, it's can be considered as a one-time watch than a must-see. However, Mantis may hold some appeal for those invested in the cinematic universe of Kill Boksoon.
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Mantis ending explained and review: Kill Boksoon spin-off delivers brutal action and strong performances but falters in story
Set in the ruthless underworld of assassins introduced in Kill Boksoon, Mantis follows the story of Han-ul, better known as Mantis, played by Yim Si-wan. He is an elite assassin, among the few killers rated “A” by the industry, alongside Boksoon. The movie begins with him returning from vacation and discovering that Cha Min-kyu, the head of MK Enterprise, has been killed.
On the other side is Jae-yi, played by Park Gyu-young. Like Han-ul, she is also a contract killer and his childhood friend who had once trained alongside him. Their bond is long-standing but complicated. Unlike him, Jae-yi has been expelled from MK Enterprise.
She carries deep insecurity about being always chosen over Han-ul, by MK despite consistently losing to her in sparring. However, Han-ul who harbors feelings for her and doesn't know about her insecurities, remains determined to stand by her side.
Dok-ko, portrayed by Jo Woo-jin, is one of MK Enterprise’s original founders and Han-ul’s former mentor. After years in retirement, he returns to reclaim control of the organization and intends to bring Han-ul back under his wing. As, he approaches Han-ul, he gives him the condition that Jae-yi must come with him which Dok-ko rejects.
So, instead of returning to MK, Han-ul chooses to leave the organization altogether and start anew with Jae-yi. She joins him, bringing along the employees from her failing contract killing company. Together, they form the “Mantis Company.”
Later, Han-ul meets Benjamin, the owner of a software firm, who offers to fund their new venture. However, during their meeting, Han-ul takes offense at Benjamin’s words and walks away. Choosing independence, he begins seeking jobs on his own, relying heavily on Dok-ko’s support, though Dok-ko has his own hidden agenda.
Cracks soon begin to show within the Mantis Company. The employees accuse Han-ul of treating them as unworthy. Meanwhile, Benjamin approaches Jae-yi with an offer. Frustrated with Han-ul for pitying her, she challenges him to a sparring match which reluctantly, he accepts. This leads to a fierce duel with Jae-yi emerging victorious and leaving the company following that.
Unbeknownst to them, one of Jae-yi’s employees records the sparring match and leaks it across the contract killer community. The video damages Han-ul’s reputation, causing his work opportunities to dry up. Left vulnerable, he becomes more dependent on Dok-ko.
Jae-yi, now partnering with Benjamin, begins her rise. With his backing, she directly challenges MK Enterprise and goes head-to-head with Dok-ko. During a meeting of contract killer organizations, she openly criticizes MK’s policies and rules.
Still, she distrusts Benjamin, who tries to control her and mocks her with the nickname “Lizard.” She is determined to use Benjamin only until she takes revenge on Dok-ko and seizes control of MK herself.
Benjamin, who also bears a grudge against Dok-ko, provokes the conflict further by sending a bloodied knife to Dok-ko, essentially inviting him to battle Jae-yi. Han-ul hears of this and tries to dissuade Jae-yi, but she refuses to back down.
Around the same time, Han-ul fails an assignment given by Dok-ko, leading Dok-ko to send him a knife as well. Desperate for guidance, Han-ul turns to Boksoon. Taking her words to heart, he makes a choice and sends the knife he has received from Dok-ko to Jae-yi, drawing all 3 of them into a final confrontation.
The showdown takes place in Dok-ko’s office at MK Enterprise. In the brutal 3-way battle, Jae-yi and Han-ul together deal heavy blows to Dok-ko, leaving him gravely injured. Han-ul, unwilling to kill his mentor, urges him to retire. Dok-ko refuses, insisting the fight must end in death. With tears in her eyes, Jae-yi delivers the fatal stab, ending his life.
After Dok-ko’s death, Jae-yi rises to power and takes control of MK Enterprise. With Benjamin no longer necessary, she hires Mantis Company, Han-ul’s company, to assassinate him. With this Mantis ends.
Disclaimer: This following review reflects the author's personal opinion and interpretation of the film. Views expressed may not represent those of others.
Mantis is a depiction of the contract killer underworld, laced with several moments of humor. For those who enjoyed Kill Boksoon, this spin-off offers an intriguing extension of that universe. The characters are pushed into extreme hand-to-hand combat, delivering some of the finest action sequences seen in recent Korean cinema.
Beyond the action, the film also excels in its performances. Yim Si-wan, Park Gyu-young, and Jo Woo-jin embody their roles with intensity, but it is Choi Hyun-wook who leaves the strongest impression.
Despite limited screen time, his portrayal of Benjamin, a privileged, spoiled dangerously unpredictable businessman is both hilarious and captivating. Every moment he appears on screen is entertaining, adding an edge of charisma to the film.
The cinematography also elevates the experience, capturing the fight sequences and emotional beats with a sharp, stylish edge. Where Mantis falters, however, is in its storytelling.
The nearly two-hour runtime drags, weighed down by a plot that feels disjointed and slow. Instead of building on the momentum of Kill Boksoon, the film struggles to establish itself as a worthy spin-off. The narrative lacks coherence, leaving the overall experience tedious and unfulfilling.
That said, for dedicated fans of Kill Boksoon, Mantis may still be worth a one-time watch. The biggest treat is Jeon Do-yeon's cameo as Gil Boksoon, appearing briefly to give advice to Mantis-a moment sure to delight fans. Overall, Mantis is not a strong film on its own, but for those invested in the Kill Boksoon universe, it might hold some value as a companion piece.
The film is currently available for streaming on Netflix.
