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)

Sana Kurata has a charmed life. Not only is her mother is a famous, award-winning writer, but she's the star of the hit TV comedy "Child's Toy" while still in the fifth grade. But Sana's biggest concern is Akito Hayama, a pint-sized hellion who's organized the boys in their grade-school class into a mass of unending noise and violence. With the help of Rei, her manager, chauffeur and "pimp," Sana is determined to win back control of the classroom from her new arch-enemy. But as her crusade continues, Sana moves further into Akito's life, and finds that he might not be entirely bad...or entirely safe.
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(Source: Anime News Network)

Sana Kurata, a child actress, faces many problems in her classroom, including a major one - her bullying classmate, Akito Hayama. Sana's outgoing and friendly nature leads her to work towards correcting all of the problems around her. Her 'meddling' irritates Hayama but at the same time captivates him, just as Hayama's gloomy nature irritates Sana and compels her to change him. As these two opposites attract each other, they face many hardships which bring them closer to a mutual understanding.
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(Source: Anime News Network)

Hisae Kumagai