Mayumi Shiba is the younger sister of Hiroshi Shiba, the main protagonist of Kotetsu Jeeg. She is depicted as a young girl with short pink hair and black eyes, often wearing a hairband. Her role within the series is that of a supporting character connected to the Shiba family. She is presented as part of Hiroshi's personal life and family circle, and the threat of harm coming to her or their mother serves as a strong emotional catalyst for Hiroshi's actions in battle, as he is fiercely protective of them. However, the available information does not provide further details about her background, personality, motivations, independent role in the story, character development, or any notable abilities. The existing sources confirm her identity as a family member of the protagonist but do not offer the depth required for a comprehensive character description.