Mito Yamada is the older sister of Hanappe Yamada and the daughter of Michiyo and Kyuta Yamada, residing with her family. She frequently teases her younger brother, especially following his fights, leading to an incident where he grabs her breast. Targeted by the demon Mephist Dance, she experiences a sexual encounter; after initial fearful resistance, she transforms, becoming demon-possessed. Demonic forces then overtake her home, where Dance restrains and whips her. During this captivity, depicted nude, she develops an enjoyment of the sadomasochistic dynamic with the demon.

When Hanappe intervenes to dismantle the demonic household, Mito and her parents oppose him, having embraced their new existence centered on demonic and sexual activities. Later, demons take Mito and her mother hostage to coerce Hanappe into surrendering holy artifacts meant to combat them. Hanappe complies, but the hostage situation proves a deception, as both women express preference for their demon-influenced life. Mito participates in taunting Hanappe, contributing to his subsequent suicide by jumping from a building. Following this event, she does not reappear in the narrative, despite other characters attempting to rescue Hanappe.

In the manga continuity, Mito similarly experiences a sexual encounter with Dance, leading to her transformation. No concrete information exists regarding her appearance or role in official spin-offs, movies, or other extended media beyond the core anime OVA and manga adaptations.