Fifteen-year-old Mitsumi Iwakura leaves her small, sparsely populated coastal town in Ishikawa Prefecture to enroll in a prestigious Tokyo high school. Her rural upbringing, marked by being one of only eight students in her middle school class, fuels her initial unfamiliarity with the city's scale and social complexities. She resides in Tokyo under the guardianship of her paternal aunt Nao, a transgender stylist, while her younger siblings back home adore her.

Driven by ambition and academic focus, Mitsumi meticulously plans her path toward becoming a prominent politician to tackle socio-economic issues in rural Japan. This goal motivates actions like volunteering as class representative. Though academically gifted and eventually a top student, she grapples with social nuances, frequently misinterpreting situations or communicating with unintended intensity. Her passionate facial expressions often appear stern or intimidating to others, a trait noted since childhood, leading to misjudgment.

Mitsumi's personality blends infectious enthusiasm with social awkwardness. She tackles tasks and relationships with unwavering effort, sometimes neglecting self-care during hyperfocus. Her earnest, unpretentious nature gradually wins over peers despite initial challenges like getting lost on her first day or vomiting from nerves. She forms significant bonds, including with her first Tokyo friend Yuzuki Murashige and Mika Egashira, whose insecurities Mitsumi unintentionally helps address. Her closest connection is with classmate Sōsuke Shima, whom she meets after he assists her. Their dynamic evolves from friendship to mutual growth: Mitsumi's sincerity challenges Shima's avoidant tendencies, while his support aids her adjustment to city life. After a period of distance following their breakup, Shima's subsequent development—confronting jealousy and self-blame—stems from her influence, though she remains unaware of this impact.

Her journey involves balancing ambition with self-acceptance. Initially perceiving her rural roots and clumsiness as liabilities, she learns to leverage her resilience ("getting back up when knocked down") and authenticity. This growth aids others: Tokiko Takamine adopts flexibility from Mitsumi's spontaneity, while Mika moves past resentment to genuine friendship. Mitsumi retains core traits like her idealism and animal motifs—pandas symbolizing her whimsy, and ducklings reflecting her "fish-out-of-water" experiences. Her journey concludes with a more integrated identity, embracing both her ambitions and the value of unplanned experiences.