"Negative Teacher Kanako" centers on Kanako Otonashi, a high school teacher whose outwardly cheerful and professional demeanor masks a deeply cynical and manipulative personality. Despite her role as an educator, Kanako harbors a profound disdain for her students, viewing them as naive and self-centered. Her interactions with them are often laced with sarcasm and veiled contempt, though she maintains a facade of kindness to avoid suspicion.

The narrative explores Kanako's dual life, juxtaposing her public persona with her private thoughts and actions. She frequently engages in morally questionable behavior, such as manipulating students for her own amusement or personal gain, and she takes pleasure in exposing their flaws and insecurities. However, her methods occasionally backfire, leading to moments of introspection and unintended consequences.

Key characters include Kanako's students, each representing different archetypes of teenage behavior. Among them is Ayaka, a diligent and idealistic student who initially idolizes Kanako but gradually becomes disillusioned as she uncovers her teacher's true nature. Another notable figure is Yuuto, a rebellious and outspoken student who frequently clashes with Kanako, challenging her authority and forcing her to confront her own hypocrisy.

The story delves into themes of authority, morality, and the complexities of human relationships. Kanako's interactions with her students and colleagues reveal the power dynamics within the educational system, as well as the ethical dilemmas faced by those in positions of influence. While Kanako's actions are often reprehensible, her character is portrayed with a degree of nuance, highlighting her vulnerabilities and the factors that shaped her worldview.

As the series progresses, Kanako's relationships with her students evolve, leading to moments of conflict, resolution, and occasional growth. The narrative maintains a balance between dark humor and dramatic tension, offering a critical yet engaging portrayal of the challenges and contradictions inherent in the teacher-student dynamic.