Naomi Orthmann is a twenty-three-year-old special investigator for the Bureau of Truth, a government agency established to oversee the management of artificial humans known as Neans. She serves as the field partner and handler for Rouge Redstar, a Proto-Nean agent tasked with hunting down a group of rogue Proto-Neans called the Immortal Nine. Naomi is characterized by her sharp analytical mind, pragmatism, and a calm, logical demeanor that grounds her partner during high-stakes missions. Despite this, she possesses a cheerful and talkative personality, often displaying a light-heartedness that contrasts with Rouge's more reserved nature. She is also a self-proclaimed military enthusiast and has a notably large appetite, frequently seen eating.

Naomi's background is marked by her employment with the Ministry of Truth, where she is entrusted with tactical planning, intelligence gathering, and monitoring Rouge's physical condition. She communicates with Rouge via a bird-shaped communicator when they are apart and is responsible for administering the nectar that sustains Rouge's energy. As the story progresses, it is revealed that Naomi herself is not fully human; she is a Nean created by the Visitors, beings known as the First. She dislikes being referred to as such and keeps this identity hidden, which complicates her relationship with Rouge and her own sense of self. Her primary motivation is to support Rouge in eliminating the Immortal Nine, but her true loyalties and objectives come into question as she is forced to choose between her duty to the Ministry and her growing friendship with her partner.

In the narrative, Naomi functions as the deuteragonist and the strategic backbone of the duo, providing intel and combat planning while Rouge executes the physical confrontations. She acts as a mentor and guardian figure to Rouge, though the secrets she keeps create tension between them. Throughout the series, Naomi undergoes development as she grapples with her own identity and agency, ultimately seeking to help Rouge of her own free will rather than as a mere tool of the Bureau. Her key relationships include her direct superior, Jean Yunghart, who oversees their missions, and the Gendarmerie investigator Ash Stahl, who views her with professional wariness. Her bond with Rouge is central, evolving from a professional partnership into a deeper allegiance defined by mutual trust and a shared desire for autonomy. Notable abilities include her tactical expertise, extensive field knowledge, and proficiency with technology, though she lacks Rouge's superhuman combat capabilities, relying instead on wits and strategy to overcome obstacles.