Hikari's roommate. She is a somewhat forceful girl who also seems to look out for Hikari, who she is in fact in love with.
Yaya is good friends with Hikari though they've only known each other for about a year once the story begins. Yaya got Hikari to join the St. Spica Choir the previous year, most likely in an attempt to give her more self-esteem which she seems to be lacking in, though Hikari did show interest in singing as well. Yaya is one of the most talented members of the choir, as noted by Tsubomi Okuwaka, though seems to need more dedication, as noted by Hikari.

She also has a rebellious side, sometimes going against school rules or what is normally accepted. However, when it comes to matters of love, she seems to be very shy about her feelings, substituing words with actions, sometimes with adverse results. Also, she rather dislikes first year students - such as Tsubomi Okuwaka - because they are noisy and annoying.

(Source: Wikipedia)