At the county fair, the boys come across a weapons store. The boys pretend their parents are dead and thus cannot afford anything, tricking the vendor into selling them several dangerous Asian weapons (with Stan having two tonfas, Cartman with two sais, Kyle with two nunchakus, and Kenny with a shuriken). They play a game where they pretend to be four ninjas, each with his own individual powers, on an imaginary adventure through South Park. In these situations, the episode's animation switches from the usual "paper cut-out style" of a South Park episode, into a stereotypical anime design, displayed in letterbox format. The boys are drawn as adults and Asian style ambiance plays in the background. After showing off their weapons to Craig and making him very jealous, the boys encounter Butters who wants to play ninja with them. The boys refuse and Butters dons his cape, bracers, and helmet to become Professor Chaos: bringer of destruction and doom.
The boys soon encounter Professor Chaos (unaware it is actually Butters) after an argument about the rules of having ninja powers. They engage in a stylized anime fight, where Professor Chaos displays his powerful energy blasts shot from his hands. Stan first shoots a jet of flame at Professor Chaos, only to have it turned back by his titanium cape. Kyle then catches the villain off guard with an icy blast from his nunchaku. Professor Chaos then retaliates by trapping the two boys in his "Web of Holding." Cartman then tries to use his powers, but realizes that Kyle had previously taken them away because Cartman tried to have too many at once. Kyle returns Cartman's powers, only to be transformed into a chicken. Finally, Kenny throws one of his shurikens into Professor Chaos' eye, defeating him. The style instantly changes from the fast-paced anime style back to regular South Park animation, showing the reality of the boys' fight with the weapons. Butters runs around wailing in agonizing pain having a shuriken lodged in his left eye.
In order to avoid punishment that would follow questions asked at a regular hospital, Butters is dressed up (badly) as a dog (using fur shaved off Sparky) and taken to an animal hospital. Unfortunately, Butters escapes on the way when the boys are waylaid by Craig and others, who have also bought weapons to play ninja with them. After an epic battle, featuring the "Let's Fighting Love" song, the boys realize that Butters is gone and join up to find him before he can tell anybody about their weapons.
Butters manages to make his way to the hospital, but his disguise fools the doctor, who sends him to the animal shelter, where other dogs urinate and defecate on him. The vet makes no attempt to treat Butters and prepares to put him to sleep, only to find that he has escaped so instead he decides to euthanize another dog. Fearing that they have lost Butters, the boys try to return their weapons to hide the evidence, but the weapons vendor does not give refunds.
Craig and the others then inform the boys that Butters was wandering around on the other side of the fair auction. Cartman, in a panic, pretends he has the power of invisibility, and takes all his clothes off so he can get Butters before the parents see him. Obviously, since he lacks this kind of power, he ends up completely naked and showing his genitals (barely, as he is so fat his belly covers all but a tiny portion of it) to the audience, with Butters stumbling on to the stage a few moments later. The boys immediately think they are in trouble but, at the protest, the people are actually angry about Cartman flashing his genitals on stage. In the meantime, Butters finally gets the medical attention he needs, thus the shruiken is finally removed and his wound is now treated with an eye patch, much to Butters' relief. Upon Cartman being berated for his actions back at the auction, Cartman says it was "wardrobe malfunction" but the boys decide to make Cartman the scapegoat and should be punished for what he did. Everyone agrees, much to Cartman's anger. Kenny, Kyle, and Stan leave the adults to deal with Cartman and learn that parents care more about nudity than violence. They transform back into their ninja forms and continue playing with their weapons.
Let's Fighting Love
The episode includes "Let's Fighting Love", a theme song that mixes Japanese and English lyrics without regard for grammar, tense or logic. This can be seen as a parody of the J-pop theme songs that are featured in many anime series, as well as "Engrish" commonly found in anime, pop music and everyday life in Japan as a whole. It is performed by series creator Trey Parker, who is an admitted Japanophile.