A high school classroom becomes the stage for a chaotic parade of bizarre, uncontrollable supernatural phenomena. Every girl in class 2-1 of an ordinary high school possesses a strange ability known as a "useless power" (無用力) — a psychic or physical mutation that only manifests in adolescent females and is triggered by specific emotions or situations. These powers are always inconvenient, never helpful: fingers turning into squid tentacles, transforming into a stuffed rabbit when overwhelmed by cuteness, hair blooming with flower-like growths when flustered, involuntary teleportation of nearby people triggered by a silly pose, or the ability to observe past events only while sleeping at school. The powers are officially classified as "adolescent female sudden-onset diverse plastic useless psychokinesis."

The story follows the daily lives and escalating absurdities of 2-1's students, supervised by their newly appointed homeroom teacher, Tsuyuura. He is a young male teacher completely unaware of the existence of useless powers until the first day of the new school year, when a fellow teacher warns him that his class contains "useless power users." Before he can process this, an incident occurs on opening day: all students except Monami Mabuta vanish from the classroom, forcing him to learn that every single girl in 2-1 carries a useless power. Tsuyuura spends the rest of the series scrambling to understand the rules, triggers, and consequences of each ability while trying to maintain order.

Central to the story is Monami Mabuta, a girl who attends class remotely via a life-sized cat-shaped robot because she was unable to transfer to the school in time due to her parents' circumstances and had been a chronic absentee during middle school. Her useless power activates when she performs a strange pose called the "One-Group Pose" devised by classmate Anderson Tomoko: anyone Monami perceives as occupying the same physical space as herself is instantly teleported to another location. She is deeply anxious about her attendance record but remains close with her classmates, frequently visiting them or having them over.

Narrative arcs focus on individual students and their useless powers colliding with everyday high school life. In one extended storyline, the baseball club faces dissolution, and the new captain Danpa Valénié struggles to save it while being thrown into chaos by her own power — any spherical object that flies toward her adheres to her body — and that of the student council president. Other notable arcs involve Yua Yamari, whose heart rate increase causes her to gain a mild X-ray-like transparency vision; Rizu Yojima, who turns into a rabbit plushie whenever she feels intense affection; and Makana Yuigasaki, whose hair spontaneously sprouts flower-like blossoms whenever she is confused. The series is structured as a collection of episodic yet emotionally resonant vignettes, exploring friendship, embarrassment, connection, and the awkwardness of adolescence through the lens of comically useless superpowers.