Bio: Chihiro is a high school student in Azumanga. She is the "ordinary" girl of the group of females students that are actually named. She seems to be friends with Kaorin. Chihiro appears the least in the series probably due to her being too ordinary for some situations.
Opinion: Being the ordinary student, she helps contrast the quirks of the other students. It's also nice to have someone who you feel you can have a somewhat normal conversation with. I also think her name is one of the better ones.