In the year 2041, Tokyo is the bounty hunter's world - crime is rampant and criminals plentiful. Milla Koroleva, with her killer looks and even more fatal shots, is out to make it big. Enter Kai Toya, child prodigy with supernatural skills, he's even willing to cook and clean - just about everyone's dream partner. That is, everyone except Milla. What ever could be holding her back? Follow this mismatched duo as they take on the most dangerous criminals that terrorise the city and unravel the mystery of Milla's past!

On the very first day that Kuze Aoi transferred to Hinomiya Academy, he finds himself facing down the barrel of a gun. He is introduced to the campus and the student body by his childhood friend Miyabi and learns about the prince and princess among students, Shitara Sagiri and Hinomiya Kuon. Sagiri is a cool and beautiful while Kuon is elegant and magnificent. After school, Aoi gets lost on campus and Kuon begins shooting at him and he's barely saved by a random girl named Atarashi Sonoko. It seems that Aoi holds a secret that is critical in a feud between two old, powerful families.

Ragna the Bloodedge is a wanted criminal with an extraordinarily large bounty on his head (well in the trillions) for attempting to destroy the Novus Orbis Librarium, and is Jin and Saya's older brother. In December AD 2199, several years after the Second War of Magic, a branch of the NOL was utterly destroyed by an SS-class rebel named "Ragna" also known as the "Grim Reaper", in an attempt to destroy the Librarium. The NOL, hoping to stop him, immediately announced the largest bounty ever, available to anyone who could capture him. Interestingly, Ragna possesses a powerful form of Ars Magus known as the "Azure Grimoire." This led the NOL, as well as the other fighters, to hunt Ragna not just for his bounty, but also his Azure Grimoire.

Lilith, the summoner who accompanied the hero party, was betrayed during the battle with the demons and suffered a serious injury because she refused the invitation of the hero. Helped by her demons, she cannot return to the country in a detour, so she decides to become a demon at the recommendation of Astaroth, the four demon kings who helped her. However, she made a slight mistake and she turned into a little girl. Even if she becomes a little girl, her magical power is not the same, but powers up! Summon the spirits and make an outstanding performance in battle and slow life!