Hiyori Hiwamura is a newly graduated university student who begins her career as a high school English teacher. She is assigned as the homeroom teacher for a class of second-year students, including the protagonist Akihito Abikura. Despite being an adult in a position of authority, Hiyori possesses an extremely shy and timid personality that makes her first impression on her students a poor one. Her voice is very soft and she speaks in a trembling manner, and she has essentially no physical strength or stamina, which contributes to a general air of fragility and vulnerability.

The central irony of her character is a complete disconnect between her true nature and how she is perceived by those around her. Because of her extreme nervousness and lack of confidence, Hiyori comes across as strange and intimidating. She uses a notebook filled with sticky notes to help her teach, a habit that leads students to spread rumors that she is putting curses on them. Her terrified, wide-eyed expression and mumbling speech make her look like she belongs in a horror movie, and she earns the nickname Kowakowa Sensei, or the Scary Teacher. Her many clumsy accidents, such as banging her head before class or suffering from a lack of sleep, only add to this unsettling appearance. In reality, she is just an incredibly anxious and sweet-natured young woman who is struggling to find her footing.

Hiyori's primary motivation is to overcome her shyness and become a good teacher that her students can respect. However, she is so overwhelmed by her new responsibilities that her attempts to do her job often backfire, creating an even more intimidating atmosphere. She practices her teaching alone in an empty classroom after school, using a stuffed animal as a stand-in for her students, which is where Akihito discovers her secret. Despite her fear and anxiety, she is deeply hardworking and feels a strong sense of responsibility for her students, even if her desperation to help frequently leads to embarrassing or compromising situations.

In the story, Hiyori serves as the central character around whom the premise revolves. Her extreme clumsiness and misfortune lead to a series of accidental, often lewd predicaments, specifically with her student, Akihito. She is frequently depicted in states of partial undress or in physically compromising positions, which serves as the primary source of the series ecchi comedy. Her inability to function effectively in everyday life, from organizing her apartment to dressing appropriately, often requires the intervention of others. Because she is so helpless, the more capable Akihito finds himself forced into the role of her caretaker and protector, trying to prevent her from accidentally exposing herself or ruining her reputation.

The most significant relationship in her life is with her student, Akihito Abikura. After he discovers her practicing alone and realizes she is not scary but just misunderstood, he resolves to help her correct the other students false impressions and become a better teacher. Their dynamic is highly imbalanced, as the adult teacher is so fragile and hopeless that the teenage student must take charge and support her. This extends beyond the classroom, as Hiyori later moves into the apartment next to Akihito, making him her neighbor and further entangling their daily lives.

There is no significant character development mentioned in the available sources, likely due to the serialized and episodic nature of the romantic comedy narrative, where her traits are repeated for humorous effect. Her notable abilities include her severe lack of most practical skills. Her defining trait is her Yowayowa nature, meaning her overwhelming weakness, frailty, and lack of stamina, which prevents her from being an effective authority figure. This physical and social clumsiness, rather than any specific strength, is the engine for most of the series events and her interactions with other characters.