Jako Amano is the leader of the Omegumi, a feared group of delinquent schoolgirls known for regularly leaving school early and seeking excitement in the mundane world. She is a prominent character in the High School! Kimengumi universe, commanding significant authority and influence within the school's social structure.

Jako is easily recognized by her long black hair and her signature habit of holding a cocoa cigarette in her mouth. Her name and personality carry a mischievous or contrary nature, fitting her role as a rebellious youth. She has a strong and cool way of speaking and acting, but unexpectedly reveals glimpses of cuteness and playful charm, making her a captivating figure. This tough exterior is a core part of her identity as a gang leader, and she has displayed rebellious traits since a very young age, including smoking even before starting elementary school.

Academically, Jako is initially disengaged. Her reputation includes routinely submitting blank test papers and having a long history of leaving class prematurely. Her motivations stem from a feeling of emptiness in the mundane, driving her group to constantly search for something more exciting. Her interests outside of delinquency include a strong affinity for disco music, which complements her bold and unconventional persona.

Despite her fierce reputation, Jako undergoes a significant transformation. Her role in the story is not just as an antagonist or rival to the main Kimengumi group, but also as a character capable of change. After encountering the teacher Masuyo Ikari, she is inspired to become a more exemplary student. This mentorship is a key relationship in her development, ultimately leading her to study abroad in the United States after graduating from high school. In her interactions with main characters like Rei Ichidou, she is involved in comedic yet character-driven storylines, often finding herself entangled in the absurd and humorous antics of the Kimengumi members.