Hoshino has black hair with a blue hue, and brown eyes. In high-school, her hair was past her shoulders. As an adult, she has it cut chin length.
When Chiaki sees her after she is off work, she is wearing a white blouse, a blue skirt, and blue heels.
In high school, Hoshino was in Yoshiyuki Hatori and Chiaki Yoshino's neighboring class, and she was on the student council. She and Hatori dated for a awhile, and the two were chosen as Best Couple at the Culture Festival. Hatori ended the relationship.
After Hatori broke off their plans for work, Chiaki goes out for the day and happens to see Hatori and Hoshino talking together. While talking, Hoshino touches Hatori's hair. Chiaki becomes concerned that Hatori is seeing her again. This causes Chiaki to get angry and blow Hatori off later, instead going to see Yuu Yanase. Chiaki asks Yuu if he remembers her, and he does, recalling some of their history from high-school. He also correctly guesses that Chiaki saw her and Hatori together.
- Yuu talks about Hoshino in a similar way to how he previously talked about Erika Ichinose, in that he describes them both as being pretty and says things that suggest a relationship between them and Hatori. This is presumably to get Chiaki to lose interest in Hatori, since Yuu wants Chiaki to fall in love with him instead.