Sever (Liu), a rogue Defense Intelligence Agency (DIA) operative, kidnaps the son of the agency's director, Robert Gant (Gregg Henry). In response, the DIA calls in former agent Jeremiah Ecks (Banderas) to find Sever and save the child.
The film also had two game adaptations for the Game Boy Advance, both First-Person Shooters. The first one, simply titled Ecks vs. Sever, was based on an earlier draft of the script. The sequel, carrying the film's full title, follows the story of the film more closely.
Ballistic: Ecks vs. Sever provides examples of the following tropes:
- '90s Anti-Hero: Sever, a gun-toting Dragon Lady dressed in black leather with a perpetual Kubrick Stare on her face and on a quest for revenge against her corrupt former employees. She isn't above kidnapping a child in order to achieve her goal, and usually gives short and cold responses to someone like "I'll Kill You!" and "Pain don't hurt."
- Action Girl: Sever.
- Backwards-Firing Gun: The Big Bad tricks a Mook into killing himself by giving him a backwards-firing pistol.
- Big Bad: Gant.
- Car Cushion: A DIA sniper meets this fate after Sever knocks him off his perch with a grenade launcher. Landing on the car causes its wheels to fly off and knock down some other DIA agents, for some reason.
- Cool vs. Awesome: The movie makes a valiant attempt to run on this trope.
- Dual Wielding: Sever does this with a pair of telescopic batons.
- Emotionless Girl: Sever goes through the whole movie with the same neutral facial expression despite all the property damage and human (and presumably animal and plant) casualties she causes.
- Faking the Dead: Gant set up an elaborate hoax to make Ecks and his wife each believe that the other died in an explosion. Sever accidentally figures out what Gant did and passes the information to Ecks. This results in Ecks and Sever eventually teaming up to take down Gant.
- Gambit Pileup: And how. There are five subplots, each equally confusing and misleading as everyone in this story has their hand in everything else.
- Hoist by His Own Petard: Gant's plan revolves around using a nanobot that can cause heart attacks. In the last scene, Sever shoots him with a bullet primed with one said nanobot and promptly pushes a button to kill him. (Gant: "All that training ... is that the best you can do?" Sever: "No. This is.")
- Jurisdiction Friction: Lampshaded by The Dragon, who threatens to usurp a local police captain unless he puts Ecks behind bars.
- Just Eat Gilligan: Or rather, "Just Tase Sever!" An early action scene relies on the idea that the Defense Intelligence Agency cannot shoot Sever in their attempt to apprehend her. (She's the only person who knows where she stashed a kidnap victim, so they need her alive.) Consequently, they try to shoot around her to pin her down so they can apprehend her. Naturally, she escapes with ease. If just one person in the DIA had remembered that tasers, tranquilizer darts, or tear gas exist, they would have ended the movie.
- Luke, I Am Your Father: Ecks eventually finds out that he has a son — Michael.
- Made of Iron: Most characters are this, or if not, they just shrug off being shot, in or near explosions and vehicle crashes without much care. Gant's reaction to Sever shooting him in the arm might be the most ridiculous, since it sets up the Hoist by His Own Petard moment above.
- Mama Bear: Sever wants revenge on Gant because he killed her husband and daughter.
- Mandatory Unretirement: A former colleague of Ecks' calls him in for One Last Job.
- Medal of Dishonor: A meta example; this film is the most reviewed film on Rotten Tomatoes with a 0% rating on the site, and with 118 reviews, it's the only one so far to have reached triple digits in review count.
- Nano Machine: A microscopic robot injected into a person's blood via a dart — and can subsequently induce fatal medical conditions — serves as the film's MacGuffin.
- Never Trust a Title: The movie is titled Ecks vs. Sever, but though said characters have a very brief scuffle after a chase scene early on, they never truly face each other as "enemies". They even end up fighting on the same side by roughly the halfway point of the movie.
- Stuff Blowing Up: The final act of the film, set at a rail yard, would give Michael Bay a run for his money.
- Television Geography: Averted. The scenes of the film shot in Vancouver are set in Vancouver in the film, which creates a Plot Hole of the U.S. agencies involved somehow being able to roam freely in Canada, a legally separate country, without repercussions from the collateral damage caused by their activities. (It's only just Hand Waved away with Ecks being assigned to "an FBI transnational task force.")
- Versus Title: Ecks vs. Sever. Except Ecks and Sever only fight each other once. Once!
- What Measure Is a Mook?: Sever guns down dozens of DIA agents and security guards over the course of the film, and not only does no one seem to care, but in the end, someone says of her, "She's a killer" — which prompts Ecks to reply, no, she's "a mother."