The Unbroken Chaos by Alex Davidson

In the year 2082, two teenagers, Chaos and Lilith, killed the woman who killed Chaos's parents. Or, so they thought. In reality, she was still alive. Two years later, they are hired as assassins to kill her, and along the way, they meet Kirina, a girl their age with special powers who had been held captive by the woman. Together with Kirina, the three teenagers go on a quest to kill the woman they thought dead, and possibly discover the origins of Kirina's and Chaos's supernatural powers.