The Lord of Nightmares also referred to as L-sama is the creator and essence of the mazoku and shinzoku. When she takes human form, it is usually in the body of a young, blonde-haired woman. She is neither a mazoku nor a shinzoku, and cannot be classified into such narrow terms.
Her true form is the Sea of Chaos, an infinite golden lagoon made of chaos, or nothingness. The Lord of Nightmares is omniscient, as everything in the worlds are made of her. In the beginning of the formation of the Sealed Systems, mana had existed in sufficient quantities throughout the nebula in hopes of spanning a system with sufficient magic to tempt the souls of the Courts to that system to be reborn. Instead, it created a flux that lead to two systems being birthed from the nebula. Mana pooled towards one side, while normal energy pooled towards the other. The effect was not only two systems, but two life forms being created in the wake of the initial formations. For Avalon, it was the birth of the Lord of Nightmares. She is not capable of being injured or destroyed, as nothing could ever be more powerful than her. Rhe reason for this is during her formation she absorbed subspace anchors originally used by Enma and Ran in their attempt to recreate Sol. Making her much more powerful than your typical New God.
Two known spells call upon the Lord of Nightmares' power: Giga Slave and Ragna Blade. While Giga Slave is the more powerful of the two (as it calls upon a far greater amount of LON's power) Ragna Blade is also very powerful. Lina Inverse is the only person known to have cast either spell.
Using Giga Slave and Ragna Blade carries risk, as both spells will rapidly drain the user's energy. Giga Slave, if cast incorrectly or with interruption, will almost certainly cause LON to be directly channeled into the user, possessing him or her and potentially destroying the entire world. This happened to Lina Inverse, but LON restricted her power to destroying Hellmaster Fibrizo, who attacked her. She later restored Lina to her previous human form when made witness to the perseverance Gourry Gabriev had in getting her back.
The possession of Lina Inverse changed the Lord of Nightmares human form to one similar to Lina’s. Lina temporarily gave the higher being form within the physical world. As such, it had also gave her a way to access the world around her such as the Sealed Systems and the universe as a whole. So when Enma once again arrived on Avalon to visit his family she sought him out to ask for a meeting with his father.