Futaba Aoi is a police officer serving at the Bokuto Police Station, first appearing when she joins the station's ranks. Her initial introduction often leads to a mistaken assumption, as she is a transgender woman; her biological sex was assigned male at birth, though her gender identity is female. This discovery forms a core part of her background and how she is perceived by others. Prior to her current assignment, Aoi worked in a vice unit where she went undercover as a decoy in an operation to catch a serial rapist. It was during this prolonged assignment that she adopted a female presentation and ultimately came to identify with it, a process she describes as having gone native. An ex-superior named Udamura Kumanosuke, who headed that sting operation, plays a significant role in this part of her past.

In terms of personality, Aoi is consistently presented as being more traditionally feminine in both her appearance and demeanor than many of the other female officers at the station. She fully embraces her identity, and her colleagues, despite knowing her history, generally treat and support her as a woman. Aoi herself articulates her identity clearly on several occasions, stating that while her body is male, her heart is female. This sense of self is a primary motivation, guiding her desire for acceptance in her professional and personal life, including her romantic aspirations. Regarding her romantic orientation, Aoi is romantically interested in men. This has led to several key emotional conflicts, such as when she developed an online romance with a man and felt deeply conflicted about revealing her identity to him in person. In another instance, a famous actor named Mr. Kitakoji proposed to her without knowing she was transgender. Despite being clearly attracted to him, Aoi rejected the proposal, an event notable for being the only time in the series she is seen wearing a male uniform.

Within the story of Full Throttle, Aoi serves as a supporting member of the Bokuto Police team. Her relationships with her coworkers are defined by their general acceptance of her gender identity, though they are also known to speculate about her romantic preferences. Before joining the police force, Aoi had a background as an accomplished athlete. She was a skilled basketball player, known for outsmarting opponents and making critical shots, which earned her many female admirers. One of these admirers continued to accept her after her transition. In the original source material, her sport of expertise is golf rather than basketball. Her abilities as a police officer, therefore, are complemented by this athletic prowess and the unique investigative experience she gained while working undercover in the vice unit. Over the course of the series, Aoi demonstrates a consistent commitment to her identity and her duties, navigating the challenges that arise from her personal life with the support of her colleagues.