Blue

The Azure in BlazBlue, is described as being the true power of the Boundary (or perhaps beyond the power of the Boundary). The Azure Grimoires are seemingly the only grimoires that have the power to tap into it. Terumi Yuuki was the one who created the fake Azure Grimoires along with the true Azure Grimoire. When Ragna's and Nu's Azure Grimoires combined, they formed the Black Beast, which was deemed a failure by Terumi. Ragna is able to access the True Azure through his imitation Azure Grimoire with the bond he has with Noel Vermillion.