Yohei Onuma is a human male of unremarkable physical appearance, lacking distinguishing features such as glasses, facial hair, or visible marks. His narrative significance lies in his familial bond with his granddaughter, Onuma Shizu, whose later affiliation connects her to Griselda—a Proto-Zoalord or Lost Number entity.

He features in the 1992 OAV *Bio-Booster Armor Guyver Act II*, though his precise role within the storyline remains unspecified. Available records do not expand on his occupation, personal attributes, or active contributions to events in subsequent adaptations, films, or related media.

Documented materials omit further exploration of his background, character development, or interpersonal dynamics beyond his ties to Shizu.