Devil

"I'll be honest with you. I'm tired. Exhausted even. I want things to reach the final curtains already...You're gonna have to give up that human flesh, whatever's left of it anyway. You'll have to sacrifice ever having the future you desired, and...your power. All of it will be gone, but in return, your flesh, bones and blood will be that of a Devil whose very waking will make the kingdom of Gehenna shudder."

- Azazel describing Devil to Amon Devil (生物の七星 (デビル), Debiru lit. Creature of Seven Stars) is a ritualistic spell created by Azazel, and the final Demon-exclusive Magic that completes the traces of the Original Demon's power and being. Alternatively known as the Seven Star Transfiguration (七星変貌, Nanae Henbō), it is the end goal and the purpose behind the creation of the Maken, Omni, and Nihil, and one of Azazel's grand plans. It is essentially a transformation that "ascends" a demon or demon-blooded individual into a "Shinma" (真魔, True Demon), the type of demon the Original Demon was.

Trivia

 * As one would expect, Devil is only possible to be used once due to its conditions.