The mankind had been faced its greatest trials they had never experienced before.
The "Black Beast", a creature that suddenly appeared at Japan. To against this overwhelming disaster, which already destroid majority of Japan, nations in the world decided to use Reactive Weapon but still didn't have a chance to against monstrous beast and lost the whole Eurasia. This was the beginning of the "Dark War", the biggest war in human history.
The weapons were being used were powerless against Black Beast and mankind have nothing left to against. This absolute ravage spread through the world, and now mankinds are being forced to live with fear of the monster comes from nowhere. However, the heroes who fought beside human, known as "Six Heroes" appeared and the situation had been changed.
With the "Nox Nyctores" which is created by Nine the Phantom, one of the member of Six Heroes, mankind finally gained effective weapon against Black Beast and started immediate counterattack. At last, mankind suppressed the Black Beast after fierced battles. This was the moment taking about 10 years ago since Black Beast appears on Japan.
However, even without the disaster called Black Beast, Dark War's wounds were even deeper than everyone's imagination, and to protect from "Seithr", harmful substance came out from Black Beast, mankind had to move their settlement to the "Hierarchical City", build on the mountains. Thus, the civilization once rely on science now become to change as the new civilization based on Ars Magus.
??After long time passed,
A.D. 2199 the 13th Hierarchical City of Kagutsuchi. A man appears in this city governed by "Novus Orbis Librarium." His name is "Ragna the Bloodedge".
SS class wanted criminal who has "Azure Grimoire" as his right arm, and attemps to destroy the Novus Orbis Librarium.