Ominous Nebula is a technique of extreme concentration were Zeldris rotates his darkness around him at immense speeds to the point of seeming invisible, creating a vortex that surrounds and attracts all living beings around him. This power makes the air flow and creates a vacuum and everything that comes in contact with it is sliced by Zeldris at a god-like speed by pure reflexes, making this technique a Full React. The attack power of the technique is virtually insurmountable as any object or person that comes into Zeldris' stance radius is instantly diced or knock away by instinct unless they possess sufficient fortitude or can destroy Zeldris' blade. The technique was powerful enough to damage Escanor in his state as The One albeit with only some cuts and bruises while in comparison Assault Mode Meliodas' Kami Chigiri had no effect.
Ludociel, leader of the Four Archangels, states that the speed of this technique surpasses even his Grace, Flash. By enlarging the demonic mark on his forehead, Zeldris can ensure that Ominous Nebula's overall power skyrockets, magnifying the power greatly, and increasing the damage dealt as well as the speed and power of the vacuum created. Whereas Ludociel, Merlin and Escanor could just about resist its original power (albeit with great difficulty), they were left helpless infront of its increased power. Even powerful demons such as Chandler and Cusack were forced to immobilize themselves to protect themselves from being drawn in by the all-encompassing vacuum of Ominous Nebula.