She is an extremely intelligent girl, dragon bearer, and Shiina's friend. A group of bullies, consisting of Aki Honda, Miyoko Shito, Hiroka Takamura, and Mihaya Ozaki, torture her when she does not get low scores on exams.
The manga and anime reveals an occasion where bullies force Hiroko to ingest worms from a beaker and a separate occasion where the same bullies shove a test tube up Hiroko's vagina. In addition, Hiroko's parents scold her for not receiving better marks, unaware that their daughter's poor grades are the price to pay for the bullies to leave her alone. Only finding solace from Shiina, she cannot approach Shiina about the bullying, but must live with it - until the day she snaps. She kills both her parents, and many of the children who where bullying her, with her dragon child. After experiencing the unfairness in Japanese society, she wishes that everything would disappear.