Hiromi is a girl Shin'ichirō's age and goes to the same high school as him. After her father died, she came to live with Shin'ichirō's family and has already been living with them for a year when the story begins. She has been in the same class as Shin'ichirō since elementary school, though despite being cheerful back then, she now acts a bit cold when living at his home. In contrast, she normally smiles and is popular at school. She often helps out with Shin'ichirō's father's work as they are low on manpower. She is a very good player on her school's girls' basketball team and is number six. It is clear that Hiromi has feelings for Shin'ichirō, but she decided to lock these feelings inside when she began living with Shin'ichirō. It is suggested that she hides these feelings because Shin'ichirō's mother told her, prior to the start of the story, that Shin'ichirō is her brother, which is later proven false. In the end of the series she and Shin'ichir starts dating.
Hiromi had brown-green eyes and long brown hair. She wears a school uniform consist of sleeves, blue skirt over white petticoat, black socks and shoes.