Reiko has a bad personality and will harshly speak to others. She doesn't moderate her speech, letting others know exactly what she's thinking, except when it comes to cute guys, then she'll start acting cutesy.
Despite being harsh most of the time, she really appreciates her friendship with Kanoko and the others; when the trip to the hot springs was cancelled, she begged her parents to call Naedoko's parents and try to change their mind. In the end the trip became a reality because Reiko's parents noticed how happy she was to have been invited.
Kanoko and Reiko seemed to only hang out together because they had the same circle of friends in the beginning, but have grown closer since then. After spending the day together during Natsukusa and Yamada's school festival and interacting using their real personalities, Kanoko started thinking of Reiko as one of her friends.
Reiko and Momoka were always ostracized by other girls during their middle school years and when Reiko transferred to Tomigaoka they seem to have become close. They go to the same high school and even though Reiko is harsh when she speaks about Momoka, she seems to really appreciate her friendship with Momoka and the others.