"Wasteful Days of High School Girl" is a slice-of-life comedy anime that centers on the daily lives of a group of high school girls attending Hanami North High School. The narrative unfolds through a series of loosely connected vignettes, capturing the humorous and mundane moments of their school life. The main trio consists of Tanaka, a self-proclaimed "bad girl" who often exaggerates her delinquent persona; Nozomu, a quiet and eccentric girl with a penchant for strange hobbies and odd behavior; and Shiori, a cheerful and airheaded classmate who frequently misunderstands situations. Their interactions are marked by playful banter, absurd antics, and a sense of camaraderie.

The series explores the dynamics of their friendship alongside other classmates, such as Wada, a studious and serious girl who often finds herself exasperated by the group's antics, and Minami, a popular and confident student who occasionally joins their escapades. The humor arises from the contrast between their personalities and the exaggerated portrayal of everyday high school scenarios, such as studying for exams, participating in school festivals, and navigating social hierarchies. The narrative does not follow a strict overarching plot but instead focuses on episodic moments that highlight the quirks and idiosyncrasies of each character.

Themes of friendship, self-discovery, and the absurdity of adolescence are woven into the series, often presented through lighthearted and comedic situations. The dialogue-driven humor and character interactions are central to the show's appeal, with each episode offering a mix of witty exchanges and slapstick comedy. The series maintains a light, carefree tone, emphasizing the fleeting and often nonsensical nature of high school life. Through its episodic structure and focus on character dynamics, "Wasteful Days of High School Girl" provides a humorous and relatable depiction of the everyday experiences of its protagonists.