Nana is introduced as the former mistress of Masahi Kaneda, the boss of a black market organ-smuggling syndicate. Dissatisfied with her position and aware of the criminal operations around her, she decides to sever ties with Kaneda and cooperate with the police, offering to testify against him in exchange for witness protection. Her background is thus defined by her intimate connection to organized crime and her eventual decision to break away from it.

In terms of personality, Nana is portrayed as short-tempered, spoiled, and deliberately provocative. She takes pleasure in making those around her uncomfortable, often by pressing them with awkward or confrontational questions. She is talkative, whiny, and prone to emotional outbursts, using her demeanor as a means of asserting control in situations where she otherwise has little power. Her behavior is often described as that of a spoiled brat, and she openly enjoys the discomfort of others, particularly the police officers and the assassin Rei.

Nana's primary motivation is self-preservation. Having betrayed Kaneda and the syndicate, she is acutely aware that her life is in danger. She seeks protection from the authorities and hopes to escape the consequences of her former life. Beyond simple survival, she also appears motivated by a desire for freedom from the abusive and exploitative environment she lived in. Her decision to steal a large sum of the syndicate's cash before turning informant further underscores a pragmatic, self-interested streak.

Within the story, Nana serves as the central witness that the Zero Department must protect. She is the catalyst for the plot, as her testimony is the key to dismantling Kaneda's operation. Initially a passive figure under police guard, she becomes more active as she is forced into close quarters with Rei. Her presence drives much of the film's interpersonal drama, as the narrative focuses on the unusual bond that forms between the two women.

Key relationships define Nana's arc. Her relationship with Kaneda is one of transactional exploitation: she was his mistress, but she ultimately betrays him out of fear and resentment. She also has a lover named Natsume, who remains in Kaneda's orbit after she leaves. Most significant is her relationship with Rei, the Zero Woman assigned to protect her. Initially hostile and one-sided, their dynamic evolves into an odd-couple pairing. Nana persistently tries to break through Rei's cold, emotionally guarded exterior. She cooks for her, engages her in conversation, and attempts to provoke genuine reactions from the normally stoic assassin. This relationship forms the emotional core of the story, with Nana's relentless energy gradually chipping away at Rei's solitude.

Nana undergoes limited but noticeable development. She begins as a self-centered, childish figure who relies on others for protection. Over the course of her time with Rei, she shows signs of genuine concern and attachment, although her core personality remains largely unchanged. Her key moment of growth comes when the police decide to abandon her protection due to political interference. Facing certain death, she must rely on whether she has earned enough loyalty from Rei to prompt the assassin to act on her behalf.

Nana possesses no combat abilities or special skills. Her primary assets are her intimate knowledge of Kaneda's organization and her ability to manipulate and annoy those around her, which she uses as a coping mechanism and a tool for interaction. Her resilience lies in her stubbornness and her refusal to be completely subdued by the dangerous circumstances she finds herself in.