She is the co-founder of the band with Iwasawa, and the band's guitarist. She is smart, energetic and loves to pick on Sekine. Mahjong is one of her other interests alongside music.

Spoiler

It is implied that Hisako and Iwasawa harbored romantic feelings for one another, as they often blushed in each other’s presence and made gestures of affection towards one another. They once inadvertently led Angel to believe that they had sex when the latter walked in on the two in Hisako’s bedroom, to Hisako’s immense chagrin and Iwasawa’s oblivion at the situation