When Keiko Furukura is a child, everyone finds her behavior strange. For example, one time when her classmates are begging someone to stop a fight between two boys, Keiko whacks one boy over the head with a spade, quickly ending the fight but alarming all onlookers. Keiko, not understanding the rules that govern social interactions, decides to just mimic others’ behavior. In 1998, during her first year of university, she takes a part-time job at a Smile Mart convenience store and loves it: the training and manual explain to her exactly how to behave in interactions with customers. When she starts work, she feels she has been “reborn” as a functioning member of society.
18 years later, Keiko is still working part-time at the convenience store. Currently, her coworkers include a 37-year-old married part-timer, Mrs. Izumi, and the manager, the eighth Keiko has worked under. To make herself look “normal,” Keiko mimics Mrs. Izumi’s fashion sense that the speech patterns of all her coworkers.
On one of Keiko’s days off, she visits her friend Miho, who is hosting a gathering. At the gathering, Miho’s friends ask Keiko whether she’s still working her dead-end job and whether she has ever fallen in love. When Keiko, uninterested in sex and romance, admits that she still works at the convenience store and has never been in love, the women exchange meaningful glances. Keiko wishes she were back at the store.
Keiko’s next day at work, her manager tells her that she’ll be helping a new employee named Shihara. Shihara, a tall and unpleasantly thin man, reacts scornfully when Keiko offers to answer any questions he may have. After she scolds him for failing to neaten a drink display like she asked him to, he claims that men aren’t meant to engage in such tasks: they’re essentially hunters, just like they were in the Stone Age. Keiko reminds Shihara that it is not the Stone Age and that in the convenience store they are all workers, not mere men and women.
Keiko’s next day at work, the manager and Mrs. Izumi complain about Shihara’s habitual lateness, bad attitude, and tendency to use his cell phone while working, which is against store policy. When Shihara arrives late, the manager scolds him. After the manager and Mrs. Izumi leave, Shihara rants at Keiko about how “lowly” the manager is. Keiko, realizing that Shihara looks down on her for working in a convenience store, asks why he sought employment at the store anyway. Unexpectedly, Shihara claims that he was looking for a wife but that none of his female coworkers or customers seem to be marriage material. Then he complains that women are all just looking for strong providers like in the Stone Age. The following Monday, Shihara is gone. Keiko soon learns that the manager fired him for stalking a female customer.
On Sunday, Keiko attends at barbecue at Miho’s where various guests criticize her for working a part-time job and not trying harder to get married. She starts worrying that society will reject her if she stays a celibate convenience-store worker. Longing for the store, she stops in on her way back from the barbecue. As she’s leaving, she spots Shihara lurking outside and drags him to a drink bar before any customers see him. At the drink bar, Shihara whines about how society treats of men like him. He also mentions that he wanted to get married so society would stop criticizing his lack of romantic relationships and so he could use his wife’s money to start an online business. Keiko, struck by an idea, suggests that she and Shihara enter into a fake relationship to avoid social scrutiny. Though Shihara initially protests, claiming he’d never want to have sex with Keiko, Keiko tells him she’s not talking about sex, only marriage, and brings him back to her apartment.
At her apartment, Keiko calls her younger sister Mami. When Keiko informs Mami that she has a man over, Mami is so ecstatic that Keiko is shocked. The following day, Shihara agrees to a fake relationship with Keiko so long as Keiko helps him hide from too-demanding society. The next time Keiko attends one of Miho’s gatherings, everyone is happy, relieved, and full of advice when she tells them she’s cohabiting with a man.
One day at work, the manager mentions that he needs to get Shihara his last pay stub, but he can’t contact Shihara. Keiko offers to help. When the manager realizes that she and Shihara are still in contact, he and Mrs. Izumi immediately start gossiping about it. They waylay Keiko while she’s working and question her about Shihara. When she lets slip that Shihara is staying at her apartment, the manager and Mrs. Izumi become enormously excited. As the days pass, the manager, Mrs. Izumi, and Keiko’s other coworkers gossip relentlessly about Shihara and Keiko. Keiko is horrified by her coworkers’ lack of professionalism and prioritization of gossip over store business.
A month after Shihara moves in with Keiko, Mami visits Keiko’s apartment unexpectedly. When Keiko mentions that her plan is working well—everyone accepts Keiko more now that they believe she’s in a romantic relationship with Shihara—Mami starts crying: she had also assumed Keiko and Shihara were in a real relationship and is devastated to learn that Keiko is still weird, not normal. Then Shihara abruptly tells Mami that Keiko is only behaving the way she is because she and Shihara had a fight about him contacting his ex-girlfriend. Mami, instantly happier, begins scolding Shihara for his “infidelity.” Keiko realizes that Mami would rather Keiko have an unhappy, normal relationship than exist in happy celibacy.
The following day, Keiko arrives home from work to find Shihara’s sister-in-law confronting him about failing to pay rent on his last apartment and leaving her to settle the debt. Then she questions him and Keiko about the nature of their relationship. Shihara tells his sister-in-law that they’re planning to get married, and that Keiko will quit her convenience-store job while Shihara sets up his online business from home.
Keiko, feeling defeated, quits her job at the convenience store. Immediately, she falls into a deep depression: eating, sleeping, and caring for herself seem meaningless now that she is no longer doing them to fuel her work at the store. Meanwhile, Shihara frenetically applies to jobs on her behalf. A month later, Keiko gets an interview at a temp agency. Shihara insists on accompanying her. As they arrive early, Shihara stops into a convenience store to use the bathroom. Keiko runs after him. When she realizes that the store employees are overwhelmed and the shelves poorly organized, she sets to work righting displays and giving advice to a grateful female employee. Keiko feels as though the store is communicating its needs directly to her. Shihara emerges from the bathroom and asks her what she thinks she’s doing. Keiko announces that she is fundamentally a convenience store worker, that it no longer matters if society rejects her for it, and that she doesn’t need Shihara. After Shihara tells her she’ll regret her choice and storms off, Keiko begins planning to secure another job at a convenience store.