Blue

The Azure (蒼) is an almighty power deep within the Boundary.

The Azure of the Abyss (深淵蒼) 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.

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. According to him, Litchi Faye Ling is being devoured by the energy as well, and that she should resist the temptation to embrace it any further.

Arakune once simplified the Azure to "bioenergy" and "memories", while according to comments dropped by Relius and Izanami, it is mostly made out of "life" and "souls". 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.

Yūki Terumi was able to obtain a small sample of the Azure and used it to create the Azure Grimoire, a fake Book of the Blue Blaze.

The perfect Prime Field Device, did not need the Azure Grimoire to become Kusanagi, because she already inherited the Azure.

Es is the Conciliator (調停者) and the guardian of the Azure Gate (蒼の門), and by the will of the Azure she guides the Azure Guardian (蒼の守護者), it means Ragna, to the gate.