Ars Armagus (術式兵装, Jutsushiki Heisō, Skill Formula Armaments) or "Armagus" is a more powerful form of Ars Magus that is used with the intent to kill one's opponent and requires a tremendous amount of seithr.
During the Dark War, in order to use armagus in the most effective way, it would need to consume a great amount of seithr which came from the Black Beast itself. With this knowledge, close range and melee weapons were the ideal type of weapons to develop. Those with high synchronicity were given especially advanced weapons. One of the most known of these types of weapons was the Sealed Weapon Izayoi. Many of the Izayoi was produced but only one or two remain today. The Sealed Weapons weren't the final stage in the Armagus' evolution and mankind created something more powerful called the Nox Nyctores, the causality phenomenon weapons. The Nox Nyctores were weapons that were made to directly combat the Black Beast and their power far surpassed every other armagus. Using armagus didn't come without risks. Many of the people that had wielded them experienced negative side effects. Some would lose their senses or become insane. The emotional affliction that came from the use of the Nox Nyctores was even greater. By the end, only a very few people had the certain synchronicity to use the Nox Nyctores, those people would later become known as the Six Heroes. With the causality weapons and ars magus, the war had finally turned in mankinds favor.