Хаясака Ока

Ouka is the twin sister of Shusui. She is the student president of Ginsei High. She and Shusui originally worked for the LXE, after the LXE fell to pieces. Ouka worked for Papillon in order to save Kazuki from getting killed. She specializes in hacking and computer engineering as well as having a sharp mind. In her profile, it says one of her "favorites" is Espresso.

(Source: Wikipedia)