Himeko Inaba is a central figure in her school's Student Cultural Society, where she holds the position of vice president. Her journey into this club began after a falling out with the president of the computer club, which she had originally joined. Unable to gather enough members to start an information processing club as she had hoped, she instead helped establish the Student Cultural Society, becoming its vice president through a simple game of rock-paper-scissors. Her family is noted to be relatively well-off, living in a large house, and she has an older brother with whom she has a complex but not entirely distant relationship.

On the surface, Inaba presents herself as calm, logical, and exceptionally skilled at gathering and analyzing information, often keeping a private database of details on her club members. She has a sharp tongue, uses blunt and occasionally vulgar language, and can be quick to react with violence to the foolish or perverted antics of her friends, particularly Aoki. She dislikes her first name, Himeko, because its meaning "princess child" feels weak to her, and she generally prefers to be called by her surname. However, this formidable exterior is a well-constructed facade that masks deep-seated insecurities and a chronic inability to trust others. She is honest about this flaw, claiming to have been born with a distrustful nature that makes her view everyone, even her closest friends, as potential enemies. This self-awareness leads to significant self-loathing and very low self-esteem, as she hates this part of herself but feels powerless to change it. Behind her arrogance is a socially awkward person who had no genuine friendships before high school, making the bonds she forms with the StuCS all the more precious, though she is loath to admit it openly.

Inaba's primary motivation throughout the story is twofold: to understand the supernatural phenomena inflicted upon the group by the entity Heartseed, and to protect the integrity of her friend group. Her analytical mind drives her to seek rational explanations and maintain a sense of control, as she dislikes situations that become chaotic or awkward. She often takes on the role of the group's strategist and leader, thinking several steps ahead to devise plans to navigate the various crises they face. Despite her claimed selfishness, she is profoundly considerate of her friends' well-being, often putting their interests and the stability of the group before her own happiness, even to the point of self-sacrifice. Her deep-seated fear of being abandoned or betrayed constantly wars with her genuine desire to trust and be close to others.

Her role in the story is that of the pragmatic and sharp-witted anchor of the Student Cultural Society. While she is the vice president, she often acts as the de facto leader, using her intelligence to analyze each new supernatural phenomenon and coordinate the group's response. She is the "straight man" to the group's antics, often the one to call out irrational behavior or punish foolishness. Her distrustful and cynical perspective provides a crucial counterbalance to the more selfless and optimistic viewpoints of other members, forcing the group to confront the harsher realities and potential consequences of their situations.

Her key relationships define much of her personal development. Her bond with Taichi Yaegashi is central. Initially indifferent to his selfless nature, she eventually develops strong feelings for him, admiring his sincerity even as it frustrates her logical mind. After being encouraged by Iori Nagase, she confesses her love to Taichi, though he initially turns her down due to his feelings for Iori. Undeterred, she refuses to give up, and her persistence eventually leads to them becoming an official couple, a relationship that significantly softens her and makes her more open, though also more prone to jealousy.

Her friendship with Iori Nagase is another critical dynamic. As total opposites, with Iori being more emotionally driven, Inaba considers her one of her closest friends, having helped her through a difficult personal situation before the story began. When they both realize they love Taichi, they become friendly rivals, with Iori even encouraging Inaba to confess her feelings. After Inaba and Taichi start dating, Iori becomes a full supporter of their relationship. With Yui Kiriyama and Yoshifumi Aoki, Inaba maintains friendships of mutual care, though she often expresses her affection through harsh teasing and physical punishment, particularly for Aoki's perverted behavior.

Inaba undergoes a significant transformation from a person who actively kept others at arm's length to someone who learns to be vulnerable. Her arc involves gradually dismantling the defensive walls she built around herself. The supernatural phenomena, while stressful, force her to confront her hidden desires and repressed emotions, leading to moments of embarrassing but necessary honesty. She slowly learns to accept her own weaknesses, such as her social awkwardness and distrust, and begins to rely on the strength of her friends rather than seeing them as potential threats. Her journey toward self-acceptance is intertwined with her romantic relationship with Taichi, which gives her the security to become a more openly caring and, as Iori nicknames her, "Dereban" (a bashful, lovestruck Inaba) without losing her core analytical strength.

In terms of abilities, Inaba is not physically strong or athletic, often lagging behind her friends in physical activities. Her true strengths are mental and practical. She is a brilliant analyst and strategist, able to process complex information and devise logical plans under pressure. She is also highly skilled with computers, having built her own desktop PC and possessing knowledge of programming and information technology. Her proficiency with data gathering and technology is so pronounced that she plans to pursue a university education in engineering and information technology to deepen her understanding of the phenomena she experienced.