Black Rukh is a dark magical energy that is the polar opposite of White Rukh which is too the namesake part of Rukh (ルフ), the cosmic magic essence that gives life to all living things, and when they die, this essence return to the huge flow (also known as "guidance") of Rukh that gives life to all subsequent beings in an eternal cycle of rebirth called "Fate".
Once a person is overcome with sadness, anger and hopelessness, their Rukh turns into a corrupted, unstable, black-colored Rukh that deviates from the main guidance in a process known as "Fall into Depravity" (堕転 Daten). Black Rukh is created when one goes against fate and tries to defy destiny. It is created from and fuels hatred and malice. The people of Al-Thamen are using it to change destiny as well as for creating Dark Metal Vessels. They hope to change the world with this. The Magi, Judar, is able to control it.
The people of Magnostadt have also learned how to use Black Rukh, but only Mogamett so far displayed the use of Black Rukh. It is possible that the magicians in Magnostadt can use it, but they do not exhibit it freely.
- The name of this concept (Japanese: ルフ, rufu) is a sort of play-on-words derived from two Arabic words: رُخ rukh ("rukh" or "roc" - a legendary mythical bird of Middle-Eastern origin) and رُوح ruuh ("soul").
- In Aladdin and the Magic Lamp from the One Thousand and One Nights, Rukhs (as birds) were the masters of the Djinn.
- The Persian term "rukh" was the original name for the rook chess piece, though it has very little connection to the mythological rukh.