Mitsuki Nagase worked as a physical education teacher at the school attended by her son, Manabu. However, after her son tragically took his own life due to relentless bullying, she decided to leave the school. The bullying was no mere joke—it was clearly malicious and cruel. Overcome with a mother's pride and fury, Mitsuki vowed revenge against her son's classmates. Using her well-trained, muscular body to her advantage, she tracked down the students' secret meeting place and resolved to infiltrate it, regardless of the danger. Her actions were not driven solely by vengeance, but symbolized her deep love for her son and her unyielding sense of justice.