"25-Year-Old High School Girl, I Wouldn't Do This with a Kid" centers on Ayako Fujino, a 25-year-old woman who, due to a series of unfortunate events, finds herself forced to repeat her final year of high school. After losing her job and facing financial instability, Ayako discovers that her high school diploma was invalid due to a bureaucratic error. To rectify this and secure a stable future, she enrolls in a high school under a false identity, posing as a 17-year-old student. The series explores her struggles to navigate the challenges of high school life while concealing her true age from her classmates and teachers.

Ayako's situation is further complicated by her interactions with her peers, particularly her classmate Ryota, a sharp and observant student who begins to suspect her secret. Despite her initial reluctance, Ayako gradually forms genuine connections with her classmates, often drawing on her life experiences to offer guidance and support. The narrative balances comedic moments, stemming from the absurdity of her predicament, with more introspective themes about identity, societal expectations, and the pressures of adulthood.

The series delves into Ayako's internal conflict as she grapples with feelings of inadequacy and embarrassment over her situation, while also highlighting her resilience and determination to overcome her circumstances. Her journey is marked by moments of self-discovery, as she learns to reconcile her past failures with her aspirations for the future. The dynamic between Ayako and her classmates, particularly Ryota, adds depth to the story, as their relationships evolve from skepticism and mistrust to mutual respect and camaraderie.

"25-Year-Old High School Girl, I Wouldn't Do This with a Kid" blends humor, drama, and slice-of-life elements to create a narrative that is both entertaining and thought-provoking. The series examines the complexities of adulthood and adolescence, offering a unique perspective on the challenges of growing up and the importance of perseverance in the face of adversity.