The Azure (蒼 Ao, Blue) in BlazBlue, is located inside the Boundary and 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. Yūki Terumi was able to obtain a small sample of the Azure and used it to create fake Books of the Blue Blaze, Azure Grimoires, with himself wielding a more refined version, but still only an imitation. Ragna the Bloodedge is able to access the True Azure through the use of his imitation Azure Grimoire along with the Idea Engine. Mu -No. 12-, unlike the other Prime Field Devices, did not need the Azure Grimoire to become Kusanagi because she already inherited the Azure.
Arakune is obsessed with finding the energy of the Azure. He hunts down those that exude the same energy or traces of the Grimoire. Coming into contact with the energy is what caused his form to degrade into the monster that he is. During his story, he manages to warn Litchi Faye Ling that she is being devoured by the energy as well, and that she should resist the temptation to embrace it any further.
It is also described as "The light from which the world sprang". Roy himself specifies it as a place where memory of the man's remembrances are kept, the place where "records" are gathered.
Azure is the place to where the souls return and sleep. It is the final destination of the soul. A necessary step in resetting and rebuilding the world, is sending all the souls of that world back to the Azure.
In BlazBlue: Centralfiction Es is the gatekeeper, and by the will of the Azure she will guide Ragna to the gate.