Ai starts off being a woobie and spends much of the series being victimized by different characters - including Koga, angry spirits, and Detective Gada. But she eventually reaches a turning point, while Misaki's on vacation, and starts to develop some backbone.
Misaki gets two, in chapter 17, when she finally meets Yuo.
The first, is when she enters the interrogation room to talk to him and sees he's surrounded by a group of his familiars. She tells them to hit the bricks and the very next panel, they're gone. Then she walks up to the guy who's manipulated dozens to commit suicide, including Haru, who was a stronger necromancer than herself, and calls him "dickless". And if you think that was just bravado, that was after having his cuffs removed.