Jiro's Mother is a minor supporting character who appears in the early childhood scenes of the narrative. She is depicted as a calm and principled parental figure living in the Japanese countryside with her young son and his sister. Her personality is characterized by a gentle but firm moral clarity. When a young Jiro returns home with scratches and disheveled clothing after defending others from bullies, she does not scold him for his disheveled state. Instead, she offers a quiet yet profound piece of guidance, reminding him that fighting is never justified. This moment reveals her role as the moral compass of the household, instilling in her son a sense of pacifism that contrasts with the violent military applications his future creations will be used for.

Her primary role in the story is to establish the protagonist's early home life and character foundation. She appears during a brief domestic scene that highlights Jiro's inherent bravery and sense of justice, traits he carries into adulthood. The development for this character is minimal, as she only appears in the narrative's exposition and does not undergo a significant arc. No notable abilities are attributed to her, as her function is purely thematic and emotional, providing a backdrop of stable, ethical support for the young genius. There are no further details regarding her background, motivations, or key relationships beyond this singular interaction.