Magic Formula Armaments (術式兵装 Jutsushiki Heisō, localized as Ars Armegis) are weapons utilizing grimoires. They use magic element to function and require high level of Magic Formula aptitude. During the Great Dark War, they were used to fight in close proximity to the Black Beast, and consumed the element which came from it. Like Arch-Enemy Event Weapons based on them, Magic Formula Armaments have various negative side effects, which include abnormalities in soul and emotional numbness.
Magic Formula Armaments are also weapons made with the use of Magic Formulas, and they are worn on the body. One of the most known of these types of weapons is the Sealed Armament: Izayoi. Many of the Izayois were produced, but only one or two remain today.