Hisae Kumagai 熊谷ひさえ

Hisae is one of Sana and Aya's school friends who stays throughout the series. When Sana forgets to attend her birthday party, she becomes very angry and tries to ostracize Sana, but forgives her later. She is linked with Gomi because they fight a lot but they are close friends. They might have an intimate relationship despite of their arguments.

(From Wikipedia)