Haruka is a former third-year student at the Hebijo Clandestine Girls' Academy who later becomes a member of Homura's Crimson Squad. She stands at 169cm tall with light brown or blonde hair styled with curled ends and a large pink bow. Her outfit consists of what appears to be pink and white lingerie, often featuring a diamond-shaped opening that reveals her cleavage and, in some depictions, leaves the underside of her breasts exposed. She wears a large white lab coat on her back, which is lined with numerous vials containing hazardous chemicals.

Haruka comes from a deeply troubled family background. Her mother was overbearing and obsessive, treating her like a living doll to relieve her own stress, while her father was a corrupt physician who showed little love for his family and engaged in extramarital affairs. The neglect and emotional abuse from her parents led Haruka to attempt burning down her own house. This act was stopped by Suzune, who intervened and instead taught Haruka her skills in puppetry. Using these newfound abilities, Haruka forced her father to confess his crimes. After this incident, she found her way to Hebijo Academy, becoming the first member to join its elite ranks and already a third-year student by the time her future teammates arrived.

In personality, Haruka presents herself as a sophisticated and refined young woman, though she has a pronounced sadistic streak. She finds the utmost pleasure in toying with her opponents, treating them as if they were mere playthings, and has a particular fondness for picking on those she perceives as weaker than herself. This explains her initial fixation on Hibari, whom she once wanted to turn into her own doll. Despite this difficult-to-read and sometimes manipulative exterior, Haruka is genuinely caring and compassionate toward those she considers her friends. Among her comrades, she acts almost like a mother figure, cradling their feelings and nurturing them. Even though she and her friends walk the path of evil as members of a rogue ninja squad, she tries to keep an open mind and encourage her companions so they do not succumb to the inevitable sorrow and pain that accompanies their lifestyle.

Motivationally, Haruka is driven by a desire for control and pleasure, often expressed through her sadistic interactions with enemies. However, her deeper motivations stem from her past trauma; having been treated as a puppet by her mother, she now prefers to be the puppeteer, manipulating others rather than being manipulated. She finds catharsis in using her skills to assert dominance. Despite this, she is also motivated by a genuine loyalty to her found family in the Crimson Squad, seeking to protect them and help them grow.

In the story, Haruka initially serves as an elite student at Hebijo Academy before going rogue alongside Homura and the others to form the Crimson Squad. Her role is often that of the tactical and scientific mind of the group, using her intellect to support her teammates in combat. She has been involved in numerous events, including helping to free other Hebijo students from brainwashing and participating in various tournaments and festivals.

Key relationships define much of Haruka's development. Her bond with Hibari evolves significantly; while initially Haruka saw the younger girl as a potential doll to control, Hibari came to genuinely befriend her after spending time at Hebijo Academy. This relationship became mutual, with Haruka showing a vulnerable side to Hibari that she rarely reveals to anyone else. In contrast, she has a hostile relationship with Yagyu, as they frequently compete for Hibari's attention. Within her own team, Haruka has a good relationship with Homura, though the leader keeps her sadistic tendencies in check. Mirai greatly admires Haruka, always referring to her as Mistress Haruka, after Haruka helped her deal with her past as a bullying victim. However, Haruka sometimes abuses this trust. She also forms a close friendship with Ryona, as the two share an interest in sadomasochism. Haruka also takes an interest in Hikage, testing various mystery potions on her to help her express herself.

In terms of development, Haruka grows from a troubled girl who attempted arson against her own family into a more stable, if still sadistic, young woman who values her friendships. While she still delights in causing suffering to enemies, she becomes more protective and maternal toward her allies, especially Mirai and Hibari. She also reconciles with her past to some degree, expressing a desire to reconnect with her mother, though the outcome of this is unknown.

Haruka's notable abilities revolve around her scientific genius and mastery of unconventional weapons. She is a prodigy in chemistry, biology, and genetic engineering, once creating a chimera that combined a snake with a carnivorous plant as a weapon. In combat, she primarily uses the various hazardous chemicals stored in her lab coat, which can freeze, poison, burn, or paralyze opponents. She is also a master puppeteer, controlling marionettes in battle. In later iterations, she has a small, hidden combat robot inside her coat armed with claws, flamethrowers, drills, and a chainsaw. Her intelligence is exceptional, enabling her to read and comprehend college-level textbooks at a young age and design complex mechanical and biological weapons.