Butters is distributing flyers for a newly opened City Sushi restaurant, giving a flyer to Tuong Lu Kim, the owner of the Chinese restaurant City Wok. Bewildered at the prospect of a Japanese restaurant next to his, an angered Lu Kim enters the establishment and starts a fight with the owner, a Japanese man named Junichi Takiyama. Butters is then sent home by the police for indirectly starting an Asian Turf War. Butters is then taken to therapy where he ends up being misdiagnosed with Multiple Personality Disorder by the psychiatrist Dr. Janus. However, it would turn out that Janus is the one with Multiple Personality Disorder and unknowingly puts Butters in situations that make the boy appear more mentally unfit.
While this occurs, Lu Kim is further infuriated that everyone in South Park is lumping the Chinese and Japanese together. He proceeds to enact a plan to get rid of Takiyama by first faking a truce and then publicly humiliating him at the school by depicting old stock photos of the atrocities Japan committed against the Chinese during World War II. He later makes an apology while building a tower between the two restaurants, intending to murder Takiyama and make it look like a suicide which would not arouse suspicion due to the stereotype that many Japanese people kill themselves over "shame". At that time, Butters is investigating Dr. Janus's house at the insistence of one of his personas and learns that Lu Kim is actually another persona of the therapist.
Butters contacts the police and as they arrive, Lu Kim is attempting to push Takiyama off the tower and visibly changes his personality in plain sight before the town. Out of shame for being fooled into easily thinking a white person was actually Asian, Takiyama ironically commits suicide by jumping over the edge of the tower and landing on the City Sushi building, destroying it on impact. Despite Takayama's harassment and death and the disorganized state of Janus's mental health, the police decide to keep Lu Kim around since he owns the only Chinese restaurant in South Park. The episode ends with Lu Kim in a prison cell, covered in a blanket, and when a fly lands on him, a voice-over can be heard where he says he'll show them he's fine as he wouldn't even harm a fly. At the end, a transparent American face, supposedly Dr. Janus' or The Evil Personality, due to the evil sounding music, can be seen on Lu Kim's, indicating that the other personalities still exist. The scene then cuts to the City Wok Chinese Restaurant.
AV Club gave "City Sushi" a "B+" rating saying: "City Sushi ended up being one of those episodes that I appreciated as a whole more than often truly enjoyed in the moment, admiring it as an overall story without finding anything specific in it that I’ll still be laughing about months later out of context—not like “Vunter Slaush,” for example. Overall, it was a bit akin to its ending, which recreated the denouement of Psycho right down to having Janus/Lu Kim repeat Norman Bates’ interior monologue word-for-word: It was clever in its execution, but ultimately lacking that extra madcap sting that pushes South Park over the edge from good to great."
IGN gave "City Sushi" a "6.5" rating saying: "This was a bittersweet episode for me, because there were flickers of brilliance scattered throughout, but nothing was consistent enough to make the story pop. I really wanted to like this episode, as I usually enjoy the Butters stories quite a bit. Right before this episode, Comedy Central aired a rerun of the hilarious "Butters' Bottom Bitch" (wherein Butters becomes a highly successful pimp), and it really made me miss the days when this series was much more consistent with its quality, which weren't even that long ago. Season 13 was lots of fun, Season 14 had its ups and downs but it was still a winner. So far this season has displayed a drastic drop in quality, and its sad when even Butters can't make it right."