Sigma (シグマ, Shiguma?) is a member of the Decay of the Angel and the general manager of the Sky Casino. 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 of eliminating the country, which they operate on by writing on both sides of the page.