‘Mantis’: Some Style, But Lacking In Substance

The very best action films often strike a strong balance between style and substance, delivering creative action sequences along with compelling characters. Action films that rely solely on action usually push the creative boundaries for sequences to make up for any lacking character work. Mantis certainly seems to have style at first, but not enough to make up for its lacking substance.

Mantis, released on Friday, September 26, 2025, on Netflix, is a South Korean action thriller directed and co-written by Lee Tae-sung in his feature debut for Netflix and produced by See At Film. It is a spinoff of the 2023 film Kill Boksoon, written and directed by Byun Sung-hyun. Mantis stars Yim Si-wan, most well-known for his role as Lee Myung-gi in the second and third seasons of Netflix’s Squid Game, as the titular character and Park Gyu-young as the second lead Jae-yi. The film also stars Jo Woo-jin as Dok-go, Mantis’ and Jae-yi’s former mentor. 

The film follows the assassin Mantis as he returns from a hiatus, encountering his friend and rival Jae-yi. The pair have ambitions to run their own company, but there is still bad blood between them due to their past. Throughout the film, the pair come to blows with how to run their company, all the while the reason for Jae-yi’s grudge against Mantis is unravelled, with their mentor, Dok-go, playing a key role behind the scenes as he tries to reorganize the assassin world.

The plot’s pacing is jarring, to say the least. The first half purely focuses on Mantis’ return to the assassin world, with he and Jae-yi reuniting and trying to run their own company, and is clearly building towards the pair having a showdown. Yet once this climactic moment comes, the film rushes through it and jumps several months, resulting in a failure to nail the emotional moments in the second half. As a whole, the second half feels muddled and stuffed with too many characters, blurring the central relationship. There’s a young billionaire character who is a simple archetype and nothing more, and as a result, the film wastes time on him that could be spent on Mantis and Jae-yi, as well as their relationship with Dok-go.

Unfortunately, the rest of the characters are not that much better. Mantis and Jae-yi are both fairly one note, only elevated by the actors’ performances. The plot dictates their actions as opposed to their actions driving the plot, which would be fine if they had more depth. Mantis’ arc of overcoming his ego feels very bare bones and predictable in comparison to Jae-yi, who goes through a more interesting story. Yet, come the second half, she seemingly achieves what she wants and thus is somewhat absent as Mantis’ life starts to go downhill in a typical second act low point. The film can’t seem to decide if it wants the pair to have a romantic or platonic relationship and as such does not commit to either. There is potential for great character drama, but the film never takes advantage of it. It ultimately culminates in a cliched instance of characters putting aside their differences and rivalry to take revenge on the bigger villain. 

The only thing keeping the characters afloat is the acting. Yim Si-wan does a good job as Mantis, giving the character an appropriate amount of wit and humor but also vulnerability and ego. His physicality for the fight scenes is commendable, and he sells each action beat. Yim is able to give Mantis some level of depth that the script lacks.

But the star of the show is Park Gyu-young as Shin Jae-yi. She excellently portrays the vulnerability of Jae-yi and sufficiently keeps up with her co-stars in regards to action sequences. She arguably gets the standout sequence when she fights multiple assassins all at once, matching the requirements physically and emotionally. There are many moments where the camera closes in on her and the audience is left to read the emotions bare on her face, interpreting the character’s thought process.

Further uplifting the drama is the score, which remains strong throughout. The score injects substance in otherwise thinly written scenes, maintaining strong tension in moments between Mantis and Jae-yi as well as making the emotional moments hit harder than they otherwise would have.  

The film does utilize strong visuals to tell its story. The colors stand out, and stylistically, the film has a distinct voice. Lee Tae-sung’s direction works well to keep the action sequences visible and dialogue scenes visually interesting. There are a handful of shots that showcase brilliant creativity, the standout example being a shot looking up at the characters after a fight with blood falling onto the lens. There are even some strong editing choices, drawing parallels between the film’s present and events prior to the film, which are shown in black and white, indicating a simpler time compared to the colorful complexity of the present.

The action sequences are mostly solid, if a bit standard. They are well choreographed, well-shot, and a few do a good job at blending emotion and violence. The sound design in each fight, though at times over the top, makes every clash of blades satisfying. However, every fight is some form of knife fight or melee battle, and whilst some stand out, mainly Jae-yi’s battle with numerous assassins and Mantis’ first battle with Dok-go that makes excellent use of household appliances, the rest of the sequences are lacking in variety. There are very few creative kills and there is only a single instance of characters using the environment and items around them to their advantage. There are also a few instances of sloppy editing in the fights, clearly meant to hide moments where the actors were unable to keep up with the stunt people.

As a result of these shortcomings in the action, the lack of substance in the plot and characters stands out more and more. What further emphasizes this issue is that there is ultimately very little action relative to the film’s runtime. At nearly two hours, there is only around twenty minutes of pure action. A tighter plot with fewer characters could have resulted in a shorter runtime and a better balance between style and substance.

Overall, Mantis is a perfectly serviceable, if mundane, action flick with strong direction, editing, score, and performances. The action itself is overall good, with strong choreography and moments of uniqueness. Unfortunately, this does little to make up for a script lacking in depth, with the plot feeling disjointed and stuffed, resulting in one-dimensional characters and rushed climactic moments. If you’re a fan of action, it may be worth watching for its style and direction alone, but there are certainly other films that strike the perfect balance between style and substance.