He comes across a dōjō led by a charismatic man referred to as "Sensei" and, after taking a trial class, decides to learn karate for protection instead of purchasing a firearm.

As Casey learns the dōjō's strange customs - its unbreakable set of rules and the praising of its powerful grandmaster, who is promoted as having developed a technique of punching through an opponent's skull with his index finger - he himself becomes more toxically masculine: looking at pornography at work, attacking his boss, and listening to loud, angry music.

Anna brutally defeats Thomas, the student promoted to black belt over her, to prove her worth, but Sensei disqualifies her for her aggression despite him usually approving of it.

He later realizes the man was innocent and returns home to find his pet Dachshund dead, kicked to death by a technique he recognizes as Sensei's.

The next morning, Sensei arrives at the dōjō to find the exiled student dead, hanging by his own belt, and he burns the body in a crematorium in the back office.

He chooses to give his position to Anna instead and, after finding his Dachshund's bite mark on Thomas's arm, has him killed by his German Shepherd, which now obeys him.

The site's critical consensus reads, "The Art of Self-Defense grapples compellingly with modern American masculinity and serves as an outstanding calling card for writer-director Riley Stearns.

[11] Peter Debruge of Variety wrote, "This singular black comedy balances off-kilter humor with an unexpectedly thriller-esque undercurrent, to the extent that audiences will find it tough to anticipate either the jokes or the dark, Fight Club-like turn things eventually take — all to strikingly original effect.