Rating: 15+ for graphic violence
Once demons were hunted down, but in modern times these same demons (also called karats) are coexisting with the human population. Keeping things under control is an organization called BIRD. One day a BIRD scientist named Senri is threatened into making a collar for a karat named Toru, who the gang leader Lawrence is using in illegal fights. Toru is tired of killing, but he suffers from a violent mental illness where his demon and human minds are separated. Knowing that he himself does not have long to live Senri takes advantage of Toru’s situation by agreeing to free Toru on the condition that he protect his daughter Tsubaki.