Created during the Dark War to combat the Black Beast within close proximity. After the war had ended, the Novus Orbis Librarium took to creating more Armagus as time went on. Like Ars Magus, they use a Grimoire and consume seithr to activate. It is important to note that not all Armegis was created during the Dark War. 
Like their successor, the Nox Nyctores class weapons, Armagus are deadly to handle, having significant side-effects for their wielders. The most famous amongst these weapons is the Sealed Weapon Izayoi, which was created as an anti-Observer armament, but had the side-effect of stealing the wielder's light, effectively making them blind after prolonged use; in some extreme cases, Armagus can kill those who wield it.
BlazBlue: Central Fiction Library Entry
- Ars Armegis
Weapons developed utilizing Grimoires during the war against the 'Black Beast.' Unlike modern weapons, they use Seithr to function. This also includes armaments worn on the body, such as the 'Sealed Weapon Izayoi.'
- BlazBlue: Continuum Shift, Story Mode, Iron Tager - Loyalty
- BlazBlue: Central Fiction, Library Mode, Weapon #023