Numen

"God is dead. God remains dead. And we have killed him. How shall we comfort ourselves, the murderers of all murderers? What was holiest and mightiest of all that the world has yet owned has bled to death under our knives: who will wipe this blood off us? What water is there for us to clean ourselves? What festivals of atonement, what sacred games shall we have to invent? Is not the greatness of this deed too great for us? Must we ourselves not become gods simply to appear worthy of it?"

- Sōzoku explaining the workings of Numen to Saitō

Princepis weild zanpakutō and have a release similar to a Shinigami's or an Arrancar's called a Numen (神を殺す人; Latin for Power of the Gods, Japanese for Deicide). Unlike Shinigami zanpakutō, who have two releases (Shikai and Bankai), Princepis only have one, although a second, rare stat can be achieved by exceptionally powerful Princepis. This is called Secundum Donum (第二祝福; Latin for Second Gift, Japanese for Second Blessing). However, as seen with Sōzoku, some Princepis may "mold" together thee states into a single powerful one, increasing their powers vastly.

While a shinigami release mostly changes the zanpakutō, and an arrancar's Resurrección mostly changes their own body, Byakkō has noted Numen to be somewhere between. However, the Aurora corrected him, explaining that Numen was something universal and heavenly, standing far above a shinigami's or arrancar's release.

Trivia

 * The name and concept of the technique, aswell as the quote, is a reference to God is dead, a statement by the famous philosopher Friedrich Nietzsche.