Kamiyama Miko is Mizuho's best friend. She is sweet, good hearted and somewhat naive. She lives in a temple with her father, and works there as a maiden.
She takes a big part on the OVA, as well as some part of the TV Serie. Several episodes features her as a supporting character, and even one, episode 10 is about Miko.
Comparing her on both TV and OVA, I could say she is the same sweet, good hearted girl. The only difference is that, in the TV Serie, she does not have such a noticeable crush for Tsuyoshi as she did for Tooru in the OVA.
Trivia: Kamiyama Miko can be literally translated as "maiden of god's mountain".