Michiyo Yamada is a married housewife and mother of two children, Hanappe and Mito Yamada, residing with her husband Kyuta Yamada in a family household. Her initial portrayal presents her as a conventional maternal figure within the domestic sphere.

This domestic existence shifts when two demons, Ophisto Bazooka and Mephist Dance, manifest through her son Hanappe's activities. Ophisto Bazooka experiences an immediate and intense attraction toward Michiyo. A significant interaction occurs when Michiyo mistakes Ophisto Bazooka's physical arousal for a bellybutton; her playful tickling inadvertently triggers a sexual encounter between them, marking the onset of her moral and psychological transformation.

Following this event, Michiyo willingly engages in an ongoing sexual relationship with Ophisto Bazooka. Her acceptance of this dynamic becomes clear when Hanappe attempts to intervene against the demons' influence. Despite his efforts, Michiyo expresses contentment with her new circumstances and rejects a return to conventional family life. Her character evolution culminates in the active embrace of a hedonistic existence facilitated by demonic entities.

No concrete information exists regarding Michiyo Yamada's portrayal or development in the manga source material beyond its explicit nature.