Ten years ago, Bruce Wayne had watched Mio, the girl he had come to love, die after he discovered that she had betrayed him and killed Matsuda, who had trained them both. However, in truth, she had survived, creating the illusion of death by entering a trance state. She returned to her master, who had been training her to become a master assassin. He was disappointed with her for having failed to act swiftly against Matsuda because she was distracted by Bruce. Even so, he inducted her into his League of Assassins for training.