Hitoha Marui is the youngest of the Marui triplets, known by the nickname "Sanjo." A twelve-year-old student in class 6-3 at Kamohashi Elementary School, she has long black hair usually tied in a bun with a red ribbon, though it frequently falls loose and messy. Her typical attire is a modest short dress worn under a sweater or jacket. Her face is often blank, but it can shift into a ghoulish, deathly glare when she feels disturbed, nervous, embarrassed, or uncertain. This frightening expression, frequently captured in unflattering photos, leads others to see her as unphotogenic. Once, during an illness, her appearance temporarily became beautiful.

Reserved, cold, and introverted, she carries a mysterious, ghostlike air. Social interactions are a struggle due to her phobia and ineptness, which thwart her desire for friends and cause her to withdraw from others, rationalizing her isolation with expressed annoyance toward her family and classmates. She fears heights, swimming, and cockroaches. She sometimes attempts to conquer her fear of swimming but dismisses the effort as pointless. Diligent and responsible, she is the most mature of her sisters, achieving perfect exam scores and managing household chores like cooking, cleaning, and sewing. She is frugal, dislikes waste, and seeks opportunities to save money or acquire free items. Despite her maturity, she retains a childish attraction to cute things like stuffed animals and forms affectionate bonds with small creatures.

Her interests include reading erotic fiction and pornographic magazines, which she conceals with book covers. Her interest is not clearly sexual, and she reacts fiercely if anyone tries to take a book from her. She is also a secret avid fan of the children's show *Gachi Rangers*, a parody of Super Sentai, but hides this enthusiasm out of embarrassment over its childishness. Her passion for the franchise sometimes overrides her frugality, leading her to spend her allowance on merchandise. She enjoys pranks, though they often fail.

Her relationships with her sisters are complex. She is frequently annoyed by their antics, particularly Mitsuba's, whom she often insults and calls a whore. She is comparatively kinder to Futaba, tolerating Futaba's habit of squeezing her cheeks. Despite her outward annoyance, she deeply cares for both sisters and will assist them in dire situations, such as when Mitsuba once physically defended her love for *Gachi Rangers*.

She shares a close bond with the class hamster, Chikubi, considering it her only friend and sole source of smiles. As its primary caretaker, she spoils it and shows it an affection she rarely extends to others. She is extremely protective, resorting to blackmail or revenge against those who threaten Chikubi, and even considered self-harm when the hamster seemed to transfer its affection elsewhere.

Her interactions with her teacher, Satoshi Yabe, involve cruelty and insults, often labeling him pathetic and unreliable. Yet she gradually develops a reluctant friendship with him, spending time under his desk for comfort and occasionally showing concern, such as when he was ill. She possesses his home phone number and a duplicated key, entering his house to visit Chikubi or watch *Gachi Rangers*. Communication issues and misunderstandings often cause mutual misinterpretations.

She forms a reluctant friendship with Sakiko Matsuoka, who mistakes her for an exorcist. Their interactions involve ghost-hunting activities that annoy Hitoha, but which she tolerates. Despite occasional extreme annoyance, she cares for Matsuoka, unconsciously using a friendly nickname and collecting get-well letters for her, though she fears being seen as a friend. Matsuoka remains unaware due to her air-headed nature.

She dislikes Miyashita, considering her a pervert and finding her highly annoying. She frequently forgets the end of Miyashita's name, possibly to provoke her, and this persists despite Miyashita's repeated attempts to befriend her.

Her relationship with Yuudai Chiba is minimal. He wishes to read her erotic book, but she refuses. Early interactions involved misunderstandings that led to protective actions from others.

Her father, Soujirou Marui, causes her embarrassment due to his suspicious appearance and frequent mistaken arrests. She is put off by him, though deep down she loves him along with her sisters.

She shows subtle growth in social areas. Initially isolated, she gradually forms reluctant friendships with Yabe and Matsuoka, indicating a slow increase in social tolerance. Her care for others, such as collecting letters for Matsuoka or apologizing to Yabe, demonstrates underlying empathy and maturity despite communication difficulties.