The Decay of the Angel is a terrorist organization that specializes as a murder association. Although few in number, including Fyodor Dostoevsky, Nikolai Gogol, and Sigma, its members all have powerful, threatening Abilities The Decay of the Angel is a terrorist organization that has long since been hiding in Japan, operating as a murder association which possesses a single page from the Book. Mushitaro Oguri explains that the Decay has a fourfold scheme with the penultimate goal.