Mantis returns to the professional-killer world of Kill Boksoon after its established structures have collapsed. Han-ul, whose codename supplies the title, comes back from a break to find an industry governed by rivalries, personal debts and competing claims to power. Being an efficient assassin does not make that new landscape easier to navigate.
His old associate Jae-yi is an important figure in the disorder. Their shared history gives their confrontations an emotional friction that the film otherwise sometimes lacks. Those encounters are among its strongest scenes: the tension involves more than who can land the next blow.
The action itself is the main attraction. Precise choreography, clear images and a strong sense of timing make the fights dynamic and hard. Whether the space is confined or the confrontation larger, the staging understands how to build physical pressure without losing the viewer.
Im Si-wan gives Han-ul a convincing presence, but the character remains cool and difficult to understand. Too little time is spent on his internal conflicts. Several supporting figures suffer similarly: their function in the underworld is clear, while their lives beyond it are less developed.
The script is solid rather than elegant. Dialogue can become a delivery system for information, and the film does not always move smoothly between exposition and action. It expands the earlier film's world without drowning in fan service, and the narrative can stand on its own. Emotionally, it feels flatter than its predecessor.
I give Mantis 3 out of 5 points. It is stylish, well-made action entertainment with some excellent confrontations. Stronger characters and a more consistent rhythm could have turned that competent package into something more memorable.