Yaeko Nishimiya raises her daughters Shoko and Yuzuru alone after her husband abandoned the family upon learning of Shoko's deafness. Her husband and his family blamed her for the disability, citing accumulated bad karma, leading to complete separation during her pregnancy with Yuzuru. Abandonment compelled Yaeko to work long hours, leaving her daughters primarily in Ito Nishimiya's care.

Yaeko initially exhibits a stern, emotionally distant demeanor marked by near-constant stoicism. This harsh exterior, rooted in trauma, manifests as "tough love" towards Shoko. Believing strength was essential for Shoko to endure bullying, she insisted on cutting Shoko's hair short for a boyish, less vulnerable appearance. She furiously intervened when Miyako Ishida, Shoya's mother and a hairdresser, gave Shoko a feminine bob cut instead, cutting it herself on the way home. Her protectiveness fueled deep resentment towards Shoko's childhood bully, Shoya Ishida. Years later, upon encountering him, she slapped Shoya, declared his actions had permanently ruined Shoko's childhood, and forbade her daughters from interacting with him.

Significant development follows Ito's death. At the funeral, overwhelmed by grief, Yaeko cries privately. She later thanks Shoya for supporting Yuzuru, signaling the start of her emotional thaw. A major turning point occurs when Shoya saves Shoko from a suicide attempt and falls into a coma. Witnessing this selflessness, Yaeko acknowledges her misplaced anger and sincerely apologizes to Miyako Ishida at the hospital. She physically defends Shoko from Naoka Ueno's aggression and confronts the emotional distance within her family. Discovering Yuzuru's photography of dead animals—intended to deter Shoko's suicidal thoughts—overwhelms Yaeko, triggering a tearful breakdown where she embraces her daughters and abandons emotional restraint.

Her relationships substantially evolve. She reconciles with Miyako Ishida, bonding over shared single motherhood experiences and later getting her hair cut by Miyako. She gradually accepts Shoya, initially tolerating his presence for her daughters' sake before genuinely appreciating his atonement efforts, culminating in her explicit apology to him. Though deeply caring for Shoko, her inability to learn sign language created a communication barrier, exacerbating their emotional distance. Her strictness stemmed from a desire to prepare Shoko for a harsh world; she later supports Shoko's dream to become a Tokyo hairdresser. Her relationship with Yuzuru was similarly strained by absence and emotional unavailability but improves as she openly expresses concern and validates Yuzuru's photography aspirations.