Hailing from the earthquake-ravaged, post-apocalyptic wasteland of Kanto, Yumi drifts homeless through a perilous landscape. Her appearance features either red or blonde hair, consistently paired with a blue mini-dress and red jacket.

During the "Harem Bomber" events, Rose's forces capture Yumi alongside Mari and other prisoners for sex-slave training. Violence Jack crashes their transport truck, enabling Yumi and Mari to escape. While fleeing through ruins, Yumi trips on a metal object, sustaining a leg injury that leaves her unable to walk despite her intact boot. As Mari tends to her wound, Yumi learns of Mari's search for her boyfriend Kenichi. In this vulnerable exchange, Yumi voices her wish for the pair to escape together. Rose’s men soon locate them, only to be slain by Violence Jack.

Rose later recaptures Yumi and subjects her to sexual assault. When Kenichi rescues both women, Yumi joins their escape. Upon overhearing Mari express deep affection for Kenichi, Yumi succumbs to jealousy over her own isolation and lack of support. This drives her to abandon Kenichi and Mari, betraying their location to Harlem Bomber and Rose. Her actions lead directly to Harlem Bomber threatening Kenichi’s execution unless he kills Violence Jack.

After Rose’s castle falls and Rose dies, Yumi appears with unexplained injuries. In her final moments, she repents her betrayal, confessing envy of Mari’s relationship with Kenichi and mourning her solitude. She dies shortly after. Unofficial fan theories suggest her death may link to injuries or illness from her assault, though unconfirmed. An alternative Manga UK dub depicts Yumi claiming Harlem Bomber coerced her through death threats before she dies upon Kenichi’s arrival.