Misa Kuroki
Koizumi’s lesbian friend who behaves as if they were former lovers. She is part of a small circle of friends who sell themselves to men with usually perverse intentions, Koizumi having become a part of the group for a while in her search for acceptance. Misa does not actually engage in sex with her “clients,” instead teasing them and using her own method to ensure the men never get too far with her.
In the manga Koizumi makes it pretty clear that they were never lovers, the attraction being fanatically one-sided. Still, Koizumi does value Misa’s friendship and the protection the girl afforded her when she was a part of that lifestyle.