Fuyuko Ameno, nicknamed "Onibaba" (Demon Hag), is the wife of Damesuke Amano and mother to Yukiko, Takobo, and Ikataro Amano. She is an imposing, physically large woman with a violent, domineering personality who regularly subjects her husband to verbal harassment, psychological torment, and physical abuse, often joined by their children. This behavior stems partly from her background as a formerly wealthy and beautiful woman who views her marriage to Damesuke as a personal downfall.

Her abuse intensifies in response to Damesuke's failures at work or in social situations, especially when his perceived inadequacies undermine her standing among other housewives. She frequently forces him into schemes aimed at improving their family's status, such as seeking promotions, purchasing luxury items, or impersonating their son for academic purposes, only to inflict punishment when these inevitably fail. However, she displays temporary affection or a gentler side when Damesuke secures financial gains, indicating her motivation is tied to material success and social advancement.

A significant shift occurs when Damesuke gains fortune after encountering Himiko Yamato and becomes president of the "No-Good Father" company. This success transforms Onibaba's behavior; she stops abusing her husband, expresses relief at his newfound assertiveness, and encourages him to reduce his workload. Her appearances in the narrative diminish as the story progresses, and she eventually dies prior to the events of the 1999 "Heisei Version No-Good Father" one-shot story.

A temporary reversal of power occurs in one instance where Damesuke psychically bends her body, mirroring her own cruelty, but this dynamic is short-lived. Her character design reportedly influenced the creation of the protagonist in "Obatarian" by Katsuhiko Hotta.