(Well... I didn't know what her backstory and name were, so I came up with my own story for her that best suited her appearance and actions)

She was once an ordinary holy being who looked like an angel, but she decided that she had to root out heresy herself. At first, she performed a real divine judgment, but over time, she realized for herself that there were too many heresies and all heretics needed to be exterminated. She killed so many heretics that the sin of hatred possessed her. She believed that her every action helped the World, and one day she decided that she was God. For such thoughts, she was banished from heaven, but she did not even notice it, she was immersed in the desire to exterminate all heretics. She saw heresy in those who were pure of soul...