Keiko is a 36-year-old woman who has worked at the Smile Mart convenience store for 18 years. Finding the outside world confusing and lacking a clear manual for social interaction, she mimics her coworkers' speech and dress to appear conventional to outsiders. She takes comfort in the predictable routines of her job, dedicating her body and habits entirely to serving the store.

Shiraha is a man in his mid-thirties who lacks a career path and struggles to fit into society. He harbors outdated, misogynistic views about gender roles and frequently complains that society has not evolved since the Stone Age. Despite his arrogance and poor hygiene, he shares Keiko's profound alienation from societal expectations.

Keiko's younger sister is a married woman living a conventional life with a newborn baby. She acts as Keiko's primary bridge to the outside world and provides her older sister with rehearsed lies to explain away her lack of a traditional career. While she appears supportive, she harbors a deep desire for Keiko to be cured of her abnormalities.

Mrs. Izumi is a supervisor at Smile Mart and a married housewife. She is a flashy dresser and an effective worker who inadvertently serves as one of Keiko's primary models for mimicking normal behavior. Keiko adopts her brand preferences to appear age-appropriate to outsiders.

The eighth manager to run the Smile Mart since it opened. He is loud and heavily focused on sales promotions. He values Keiko's reliability as an employee but applies traditional gender expectations when judging his staff's worth.

Sugawara is a temporary employee at Smile Mart who sings in a band. She is blunt and expressive, providing another template for Keiko's constructed personality. Keiko incorporates aspects of Sugawara's casual speech patterns into her own vocabulary.

Miho is Keiko's friend who lives in the neighborhood where they grew up. Having reconnected with Keiko at an alumni reunion, she occasionally invites her to social events. Miho lives a conventional life and pities Keiko's single status.

Yukari is a married woman in Keiko's social circle. She is observant enough to notice that Keiko's speech and clothing have changed over the years, though she fails to realize Keiko is actively mimicking others.

Satsuki is a woman in Miho's social circle. She engages in standard societal small talk, asking Keiko personal questions about her love life that force Keiko to rely on rehearsed lies.

Shiraha's sister-in-law is a severe, pragmatic woman who manages her family's finances. She uses a tracking device to monitor Shiraha's location after covering his unpaid bills, demanding that he get a proper job.

Tuan is a new employee at Smile Mart. Like the rest of the staff, he quickly begins to absorb the characteristics of the store and its workers, soon adopting their tendency to ask intrusive personal questions.

Yutaro is the infant son of Keiko's sister. To Keiko, he initially looks like an alien, representing another confusing aspect of conventional human behavior that she cannot instinctively understand.