The story of Chaos Legion is a gothic opera which occurred around 791 A.S. (aka "Anno Satanis" for some gamers). The protagonist is a Knight of the Dark Glyphs, Sieg Warheit, who is on a quest to find his former friend Victor Delacroix, who has stolen the forbidden book Apocrypha Of Yzarc, and stop him from releasing the spirit Azrail who will destroy the three plains of existence (Nether World, Middle World and Celestial World). Delacroix felt that Sieg is responsible for the death of his girlfriend Siela Riviere, and is intent to bring Sieg into a pure pandemonium that Delacroix himself has prepared as retribution not only for the sins of Sieg alone, but for the sins of the whole world. This armageddon is Delacroix's so-called Purification of the World, using relentless hordes of hideous monsters to cleanse the world of sinners.