Shihouin Mari was one of the Bravers, Code Named: Metamorph. She killed Kaidou Kanata, because he had killed and then sold her mother's organs. After she was arrested, Rikudou Akira staged her death, and than brainwashed her to work for him.
Her cheat-like ability is Metamorph, which gives her the power to take someone's else form. It also allows her to perfectly replicate her target’s fingerprints, retinas and even their vein patterns.