Hiyori is Zen Kirishima's only daughter; she's a preteen (10-12 years old), and currently attends primary (secondary?) school.

She loves her father very very much, and has a good relationship with his partner, the protagonist of this story, Takafumi Yokozawa, and often refers to him as "Yokozawa-oniichan" or simply, "onii-chan".

She had a mother, Zen's previous wife, Sakura, but she unfortunately died when she was young, and it's been noted that she resembles her mother a lot.