Akemi Hinazuki is the mother of Kayo Hinazuki and a central figure in the tragic circumstances surrounding her daughter's life. She is a woman shaped by her own history of suffering, having been in an abusive marriage with Kayo’s father. After her mother forced her to divorce him, she was left to raise Kayo alone, becoming estranged from her own family in the process. This background is crucial to understanding her character, though it does not excuse her actions.

In terms of personality, Akemi is portrayed as a deeply cruel, unstable, and sadistic individual who takes out her anger and frustration on her daughter. She exhibits controlling and obsessive behavior, keeping Kayo isolated from social contact and reacting with rage when anyone attempts to intervene. She is also a coward, as seen when she flees from child services and social workers rather than face the consequences of her abuse. Despite her violent outbursts, she is not depicted as a mastermind but rather as a broken person whose trauma has manifested as monstrous behavior toward the most vulnerable person in her life.

Her primary motivation is to maintain control over Kayo while hiding the evidence of her abuse. She regularly beats her daughter, leaving visible bruises, and then forces Kayo to conceal her injuries. In one instance, she dunks Kayo’s head into a sink of cold water, claiming it will help the wounds heal faster so that she will not be blamed. She also locks Kayo in an unheated outdoor shack as punishment, even in freezing temperatures, which directly endangers her life. When Kayo begins to find friendship and protection from Satoru Fujinuma and his mother, Sachiko, Akemi’s rage intensifies, and she tries to physically attack Sachiko with a shovel.

Within the story, Akemi serves as a primary source of conflict and a representation of the systemic failures that allow child abuse to continue. She is the reason Kayo is withdrawn, friendless, and vulnerable to a serial killer who preys on neglected children. Her role is to embody the immediate, domestic danger that Satoru must overcome to save Kayo, even before confronting the larger murder mystery. Her key relationships are defined by this abuse. Her connection to Kayo is one of tormentor and victim, while her relationship with her own mother is marked by estrangement and regret, eventually leading to her mother taking custody of Kayo.

Akemi undergoes a significant defeat but little personal redemption. In the final timeline, after Satoru and his allies successfully expose her abuse to authorities and her own mother, she has a complete breakdown. Her parental rights are terminated, and Kayo is taken away to live with her grandmother. Akemi is left screaming and crying, having lost everything, and is presumably arrested. While the series shows a flashback of her own victimhood, suggesting a cycle of abuse, her primary development is the loss of her daughter and her removal from the family unit, rather than any genuine change of heart.

Akemi possesses no supernatural abilities. Her power comes from her position as a parent and the societal expectation that a mother is a caregiver, which allows her to hide her cruelty behind closed doors. She uses manipulation and intimidation to control Kayo, forcing her to lie to protect her abuser, and shows a cunning ability to try and evade the authorities when they come to investigate. Her most notable "ability" is her successful, yet temporary, concealment of a horrific home life from the outside world.