O-Nobu appears as a young woman characterized by her black straight hair arranged in a Nihongami hairstyle, detailed with specific ornaments: a tsumami kanzashi pin featuring buratsuki or shidare elements, birabira kanzashi, and a kanoko at the base of her hair bun. Her physical description includes pale fair skin and reddish lipstick applied to the bottom of her lips. She consistently wears various yukatas or kimonos, each fastened with an obi belt tied at the back, and Geta footwear. Her background establishes her as the heiress to an herb merchant family, placing her in a higher social class than her childhood friend, Yunoshin Mizuno, who comes from a lower-ranking samurai family. This class difference prevents a formal relationship between them despite their mutual affection. Her merchant heiress status shapes her social position and influences Yunoshin's decisions. O-Nobu shares a significant emotional connection with Yunoshin. Prior to his entry into the Inner Chambers, he visits her to say farewell and kisses her. This act underscores their bond and highlights the personal sacrifice Yunoshin makes by leaving. Her feelings for him and her reaction to his departure represent a pivotal moment for his character motivation. Her character primarily serves to establish Yunoshin's pre-Ooku life and emotional stakes.