Natsuki appears in the prequel manga and anime Bad Company, which depicts the middle school years of Eikichi Onizuka and Ryuji Danma before the events of Shonan Junai Gumi. She is a former member of the Running Wild Angels, a prominent bosozoku biker gang led by Masaki. Her background is marked by a violent past connected to the gang. She is presented as a confident and mature older woman who captivates Ryuji Danma with her femininity and worldly demeanor. After learning that Ryuji has been locked out of his home, she gives him her Honda CBX motorcycle, an act of generosity that inadvertently draws him into the unresolved conflicts of her previous life. Her primary motivation stems from a desire to escape or settle the violent history she carries, particularly her abusive relationship with her ex-boyfriend, Akira Nezu, who claims ownership of the CBX and physically assaults her. In the story, Natsuki functions as a catalyst for Ryuji's emotional growth and the central conflict of the second part of Bad Company. Her role is that of a love interest whose dangerous past forces Ryuji and his friends into a confrontation with Nezu. The most significant relationship she has is with Ryuji, whom she trusts with her motorcycle and personal history, and her antagonistic connection to Akira Nezu, whose abuse she endures until the breaking point. Her development culminates in a moment of desperate self-defense when she stabs Nezu during a confrontation, leading to her arrest. Although she is later released because Nezu's injuries are minor, the experience forces her to leave and separates her from Ryuji. The story ends with Ryuji maintaining her motorcycle in anticipation of her return, implying a lasting bond. In terms of notable abilities, Natsuki is a capable motorcyclist and possesses the resilience and street awareness typical of a former bosozoku member, but she is not depicted as a fighter; her strength is more emotional and symbolic, representing a link to a wilder past and the possibility of a different future.