The unnamed 14-year-old protagonist is a middle school student who suffers from a lazy eye. This physical trait causes him poor depth perception and frequent headaches, and it makes him the primary target for intense physical and psychological bullying by his classmates. Quiet and highly self-conscious, he lives with his caring stepmother and frequently absent father, seeking a way to understand the seemingly senseless cruelty of his peers.

A middle school girl who initiates a secret correspondence with The Narrator. She is mocked by classmates for being unkempt and smelling bad, earning her the nickname "Hazmat." Despite living in a wealthy household with her mother and stepfather, she intentionally maintains her messy appearance as a show of loyalty to her struggling biological father.

The popular star student of the middle school class. He leverages his high social standing to torment vulnerable classmates without fear of intervention from teachers or peers. His abuse is calculated and cruel, often involving physical humiliation, and he sets the standard for how the rest of the class treats the outcasts.

A member of Ninomiya's friend group who actively participates in the bullying. Unlike a standard unthinking follower, he possesses a sharply defined, nihilistic philosophy about the world. He views the school's social hierarchy as chaotic and meaningless, justifying his aggression simply as an exercise of personal willpower and convenience.

The Narrator's primary guardian, as her husband frequently travels for work. She moved in when The Narrator was young and has since cultivated a warm, supportive environment for him. She provides a safe, quiet space away from the hostility of his middle school life.

The Narrator's biological parent. He spends almost all of his time traveling for business, leaving his wife and son to manage the apartment alone. When he is home, he remains quiet and largely detached from his family's daily lives.

Kojima's biological parent, who lives in a seaside spa town working as a driver for masseuses. He lost his business and fell into severe debt, which led to the dissolution of his marriage. He remains a source of intense pity and devotion for his daughter.

A woman who divorced her struggling husband after growing tired of pitying him. She has since remarried a wealthy man and adopted a luxurious lifestyle, actively discarding any reminders of her past poverty.

Momose's younger sibling. Her brief appearance reveals a softer, more protective side to her brother, contrasting sharply with his cruelty toward his classmates.

A medical professional who treats The Narrator's injuries. He casually introduces the possibility of corrective surgery for the boy's lazy eye, presenting a simple medical solution to a deeply personal and philosophical dilemma.