Wasteful Days of High School Girls follows Akane Kikuchi as she arrives at Sainotama Girls' High School for her entrance ceremony, still thinking about the childhood dream of becoming a manga artist that she has never really pursued. She soon discovers that she has been placed in the same class as her two best friends: the deadpan, emotionless Shiori Saginomiya and the loud, ridiculous Nozomu Tanaka.
Tanaka immediately faces the reality that her elementary-school dream of becoming popular with boys and finding a boyfriend is impossible at an all-girls school, so she starts badgering the other students to set her up with their male friends. Instead, she finds herself surrounded by a class full of eccentrics. There is a grandmother-loving loli, a reclusive chuunibyou, and an overly analytical stalker, each one bizarre enough to earn a nickname from Tanaka that captures their particular brand of weirdness.
From that point on, the series turns their ordinary school days into a nonstop parade of chaotic conversations, absurd misunderstandings, and tiny daily dramas, all set in a comedy that begins each time with Tanaka's favorite opener: "Hey, wanna hear something amazing?"