Edogai's Mother is a deceased character whose presence looms large over the taxidermist Yasaku Edogai. She lived with her son in their home and workshop in Yubari, Hokkaido, after the family relocated from Nara Prefecture. The dry and cool climate of Hokkaido was better suited for taxidermy work, which was the family's trade.

During her life, Edogai's Mother exhibited a profoundly abusive and controlling personality. Her behavior was a central factor in shaping her son's disturbed psychology. She murdered her own husband, Edogai's father, and also subjected her son to extreme physical abuse, including castrating him because she believed he was becoming too much like his father. She consistently tried to isolate Edogai from others, telling him that no one loved him and that all men were bad. Her motivations appear to have stemmed from a deep-seated paranoia and a desire for absolute control over her son, using manipulation and cruelty to keep him dependent on her.

Edogai's Mother eventually died of a heart attack. Following her death, her son preserved her corpse using his taxidermy skills, keeping her body seated in their home as if she were still alive. This act was a manifestation of his inability to break free from her control, and he began to suffer from auditory hallucinations, hearing her voice and the voices of other deceased individuals as though they were still speaking to him.

Her role in the story is primarily as a psychological antagonist to her son. She appears only as a preserved corpse and as a voice in Edogai's head, constantly berating him and commanding him to be hostile towards visitors. When Lieutenant Tsurumi of the Seventh Division arrives to recruit Edogai, her voice urges her son to kill him. It is only through Tsurumi's manipulation that Edogai finally breaks free. After one of Tsurumi's subordinates, Kohei Nikaido, desecrates her corpse, Tsurumi hands Edogai a gun and encourages him to "leave the nest." In this pivotal moment, Edogai shoots the stuffed corpse of his mother, which silences her abusive voice in his head and marks his psychological liberation from her influence.

The character's development is static, as she is already dead before the main story begins. However, her son's development is directly tied to overcoming her. The act of shooting her corpse is the climax of their relationship, allowing Edogai to finally declare that she died of a heart attack and that he should have settled matters with her while she was still alive. This event frees him to fully devote his taxidermy talents to Tsurumi's cause. She has no notable abilities of her own, as her influence is entirely posthumous and psychological.