The story of Chaos Legion is based on a light novel of the same name, written by the Japanese author Tow Ubukata. The events begin in the year 791 A.S. (Anno Satanis). The protagonist of the game is a Knight of the Dark Glyphs named Sieg Wahrheit. His best friend, Victor Delacroix, blames him for the death of Siela, Victor's sister and Sieg's lover. Unable to contain his despair, Victor decides to 'purify' the sins of the world by unleashing hordes of monsters and finding three sacred glyphs to resurrect the evil spirit Azrail, who would eventually obliterate all existence.