There are some people who have an inherent ability to take a life without any second thoughts or guilt, despite appearing to be timid. These emotionless killers are referred to as "Innocent Devils," and rely solely on their instincts.
The plot follows Touko Kamijou, a small but talented criminal psychologist, who views the Devils as the next step in human development. She is accompanied by Akane Shinkai, a young girl who lost her parents to a Devil eight years prior. The two of them work together to explore the world of these murderers, with the ultimate goal of helping Akane understand the complex emotions that come with taking another person's life.
