Hitomi is a character who appears across multiple adaptations of the Appleseed franchise, including the original manga, the 1980s OVA, the 2004 film Appleseed, its 2007 sequel Appleseed Ex Machina, and the 2011 series Appleseed XIII. She is a second-generation Bioroid, a species of genetically engineered humans created with suppressed emotional capabilities to serve as a stabilizing influence on society due to their inability to feel hatred or intense anger.

In terms of background, Hitomi was created using genetic material from Carl Knute, making her biologically related to the series' protagonist, Deunan Knute. Like other Bioroids, she was born with pre-programmed knowledge; in her case, she was educated prior to birth in political sciences, which accounts for her ability to rise to the position of Vice Minister of Olympus. Her exact chronological age is ambiguous. Though she appears to be in her mid-to-late twenties, as a Bioroid she was born as a teenager, and some sources suggest she could be decades older due to life-extension treatments.

Hitomi's personality is marked by a cheerful, childlike demeanor. Her Bioroid nature regulates her emotional range, leaving her genuinely fascinated by human experiences, particularly the concept of love, while being deeply disturbed by expressions of hatred, especially when directed at Bioroids by human soldiers. In the source manga, this social awkwardness is sometimes addressed through her use of a customized book titled Human/Bioroid Interactions for Bioroid Hitomi, which she consults to navigate everyday conversations and understand common idioms.

Within the story, Hitomi serves as a bridge between different worlds. She is a recruiter for ESWAT, the elite counter-terrorism unit of the utopian city of Olympus, tasked with identifying and bringing talented individuals into the organization. Her most significant act in this role is leading the mission into the war-torn Badlands to rescue Deunan Knute and her partner Briareos Hecatonchires, thereby introducing them to Olympus and setting the entire plot of the 2004 film and other adaptations into motion. She also helps Deunan acclimate to her new life in the city.

Her key relationships are primarily with Deunan, Briareos, and a mechanic named Yoshi, who is her boyfriend in some iterations. She is a close and loyal friend to the two protagonists, often acting as a source of information, support, and comic relief. Her biological connection to Deunan's father creates an underlying familial bond between the two women.

Her development is often tied to the central conflicts of the various stories. In the 2004 film, her life is threatened when she delays a required life-extension treatment at a Bioroid care center, only for that center to be destroyed by terrorists. To save her life, Deunan must activate the "Appleseed" data, a genetic key created by her mother, Dr. Gilliam Knute, which reactivates Hitomi's dormant reproductive functions and frees her from dependence on constant treatments. In the original OVA, she becomes an unwilling pawn in a plot to deactivate Gaia, the central AI of Olympus, because her unique DNA is the biological key required to shut it down. This trait, her genetic code functioning as a master password for critical systems, is a recurring element, as her name is also used as an access code to disable rogue mobile fortresses.

Hitomi possesses several notable abilities beyond her role as a political operative. As a Bioroid, she has enhanced physical capabilities and a high IQ. Her DNA itself functions as a biological key, or "Barrier Maiden," for the supercomputer controlling Olympus, making her a target for antagonists. She is also intelligent and resourceful, as seen in Ex Machina, where she assists Briareos in an investigation by helping him uncover missing data about a cyborg doctor, a quest that ultimately leads to her being taken hostage.