Hiyori is a tiny, blonde-haired girl who wears her hair in pigtails. As a Vizard, she wears a red jogging outfit decorated with the first kanji of her name. She also has an overly long fang protruding from the left side of her mouth. This physical characteristic has caused both Ichigo and Shinji to call her "snaggletooth" in the English dub. As a result of her thorny disposition and possible insecurities, Hiyori never seems to display much emotion besides anger, and always appears to be frowning. When Hiyori was a Lieutenant she wore a standard Shinigami uniform with the standard 12th division armband to signify her rank on her right arm. During her days as a lieutenant, her pigtails were fairly long and hung down. During the current timeline, they are shorter to the point of being stubby.
Despite her small size, Hiyori is an aggressive and short-tempered girl with rather violent tendencies. Her most common victim being Shinji Hirako, whom she frequently abuses, usually by smacking him with one of her sandals. She has even made it a reflex to use him as a human shield when necessary, and show him an obvious lack of respect, a gesture that he seems to return. This behavior dates back to her time as a Lieutenant, despite the fact that Shinji outranked her back then. She shows very little respect to the majority of people around her, easily losing her temper or getting into fights. Having viewed her former Captain Kirio Hikifune as a mother figure, Hiyori was quite hurt by her departure and initially refused to accept Urahara as her replacement, even treating him with her trademark violence and disrespect, despite his attempts to be her friend. When Kirio Hikifune was in charge of her, Hiyori was very respectful to her old captain as a sign of respect and trust but still smacked everyone else around. Hiyori also seems to harbor a hatred of both Shinigami and humans, which she noted in a rare quiet moment with Shinji, implying she has some major identity issues. It could also be said that her violence is a form of defense mechanism.
After Ichigo started to train with the Vizard, she shifted all of her temper on to him and switched back once Ichigo left. Hiyori is the one who makes Ichigo pass the test but he nearly killed her with one hand and all the other Vizard had to intervene. She got him to train on her "super walker" though he quickly lost his temper, believing the training to be a waste of his time. She seemed to be worried when he fought his inner Hollow, unusually quiet and serious. Rose said she was quite happy of Ichigo's appearance in their group because their family was growing as Hachigen Ushōda is happy to see Orihime Inoue. During her time training, she never succeeded in making Ichigo call her "Hiyori-san" (Miss Hiyori). She calls Ichigo a "dumbass" in the English dub during their interactions and preview segments probably as a method to reflect her aggressive mannerisms.
Hiyori was the former Lieutenant of the 12th division before the development of the Shinigami Research and Development Institute. She served under Hikifune before her promotion, and later under Urahara her replacement. Although she initially refused to accept him as her previous Captain's replacement, Hiyori stays at her post and agrees to serve her new Captain. Following Urahara to a Soul Society prison, he explains to her the policies of Soul Society concerning the prisoners. He tells her that anyone who Soul Society believes to be a danger to the peace is locked away in the prison ward, but shares his dream of building a new institution within the 12th Division with the help of the most dangerous prisoner, who is no other than Mayuri Kurotsuchi. Although initially appalled by the idea of locking people up for virtually no reason, Hiyori agrees to help him, and participates in Urahara's creation of the Shinigami Research Institute. During her brief time as a member of the institute, Hiyori served as a lab manager, while clashing with then Third seat Officer Mayuri Kurotsuchi, over who has more authority under the Captain.
She was eventually dispatched by Kisuke Urahara to investigate the disappearances in the Rukongai, but is attacked by the unfortunate victims of Sōsuke Aizen's Hollowfication experiments. Struck from behind by Kaname Tōsen, she soon faces the same fate as her comrades, and begins to transform into a Hollow. Although Kisuke Urahara attempts to stop Aizen and save the victims of his twisted experiments, Aizen escapes and frames Urahara for the crimes. Kisuke Urahara uses the Hōgyoku in an attempt to save Hiyori and the others, but they are soon forced to flee Soul Society, or be dealt with as Hollows.