Yūko is a middle school science teacher and single mother who decides to retire following a personal tragedy. She struggles with the limitations of the Japanese juvenile justice system and adopts a cold, calculating approach to addressing the students she holds responsible for her loss. She possesses a keen understanding of classroom dynamics and student psychology.

Mizuki is the class president in Moriguchi's former homeroom. She possesses a highly logical mind and refuses to participate in the mass bullying occurring in her classroom. Her empathy makes her an outlier among her peers. She actively tests assumptions rather than succumbing to group fear.

Shūya is a highly intelligent student with a passion for electrical engineering and creating inventions. He feels alienated from his peers, viewing them as intellectually inferior. He harbors a deep desire for attention from the maternal figure who left his family years prior.

Naoki is a middle school student who struggles academically and athletically. He relies heavily on the approval of others and is highly sensitive to perceived slights from teachers and peers. Following a major classroom incident, he retreats to his bedroom and refuses to bathe, obsessing over physical preservation.

Mrs. Shitamura is a traditional housewife who places immense pressure on her family to maintain a perfect public image. She spoils her son while burdening him with heavy expectations. She directs her anger outward when her family faces difficulties, often writing complaints to the school.

Werther is a young, inexperienced teacher who takes over Moriguchi's science class. He idolizes a famous former educator and attempts to emulate his passionate teaching style. However, his efforts often come across as patronizing. His failure to read classroom notes leaves him ignorant of the severe social dynamics among his students.

Manami is Moriguchi's four-year-old daughter. She frequently accompanied her single mother to the middle school due to limited childcare options. She loved a cartoon character named Snuggly Bunny and enjoyed feeding a stray dog near the school swimming pool.

Masayoshi is a passionate educator with a troubled past as a gang leader. He believes strongly in the rehabilitation of youth. A medical diagnosis forces him to end his engagement and step away from his planned family life.

Kiyomi is one of Naoki's older sisters. She lives away from the family home and attempts to understand the dysfunction within her household by reading her mother's personal writings. She provides an outsider's perspective on the suffocating environment her brother endures.

Shūya's mother is a gifted electrical engineering professor. She initially gave up her career for marriage and motherhood, which led to deep resentment and abusive behavior toward her son. She eventually leaves the family to return to academia.

Shūya's father is a man who runs an electronics store. He gains full custody of his son following a divorce. He subsequently remarries and starts a new family, leaving his older son to occupy an unused property alone.