When he was a young boy, he was saved by Kurohime and began to admire her. At the same time, his belief of "the gun is the sword of justice" began. In the ten years that passed before he met Kurohime again, his skill at the quickdraw earned him the nickname Zero of the Superfast Quadruple Guns due to his fighting style of using four revolvers at once.
After he met Kurohime again he vowed to protect her as she protected him, and to break her curse.