Starting her dream job as a math teacher at Shirokin Academy, Kumiko Yamaguchi exudes intelligence and enthusiasm. However, her first day reveals atrocious students and cowering teachers, causing her to realize that the all-boys high school is filled with delinquents who have no desire to better themselves. Despite her quirky persona, Kumiko conceals a secret that her rowdy pupils are unaware of - she happens to be the clandestine leader of a powerful yakuza clan and possesses remarkable fighting skills. To maintain her job, Kumiko must keep her impressive strength and criminal influence hidden. Nevertheless, with the vice principal's persistent attempts to oust her and Shin Sawada, the head of her class of misfits, suspecting her of being stronger than she appears, Kumiko faces a challenging career as a teacher.