Blue Grimoire

The Azure Grimoire in BlazBlue is the so-called "strongest" grimoire, also known as the "original codex" and can tap into the power of the Azure.

Information
Despite being called a grimoire, its form is not that of a book, but rather a high-density mass of concentrated seithr similar to the Black Beast. It has no fixed form and is currently imitating the right arm of Ragna the Bloodedge. Because it requires life force to function, Ragna absorbs life from other people. In actuality, Ragna's grimoire, along with Nu (v-13)'s is only an imitation. Terumi Yuuki was the one who created the Azure Grimoire. Terumi said that the Azure Grimoire's original form was a cauldron. The purpose of the Azure Grimoire is to gather souls.The Azure when released also has the ability to grant sevral advantages to its owner increasing their stats, producing a magical gylph to strain the enemy and doubles it's user attack power as seen with the perivous three user Ragna, Terumi and Nu.

Terumi is the one with the true Azure Grimoire, so he is the one that has to gather the souls, and judging from what's been stated about smelting a Nox Nyctores, it takes thousands and thousands of souls. The reason the cauldron of Kagutsuchi is there is because it is where the 13th Anti-Sankishin unit, Nu was smelted. When the cauldrons are activated, a space time continuum is created to form a protective coccoon for the medium, and that's presumably the force for the Black Beast's time travel. At Adventus there is no cauldron, just Terumi's Azure Grimoire, because he can use that to temper Mu without a cauldron.