Mukai

Mukai (無解, "Nothingness Release") is a unique state that a Zanpakutō may achieve by tapping into the darkness of a Shinigami's soul that was once a part of the Amatsu-Mikaboshi. It is known to be the secret weapon of L'Obscurité.

Overview
Upon the destruction of the force of the absolute primordial darkness known as Amatsu-Mikaboshi, due to the movements of "In" (陰, Yin) and "Yō" (陽, Yang) in Shinto belief, the Mikaboshi was said to have been all but gone, its residue still lingered on in the hearts of all beings and is allegedly the cause of all human passions.

During the years prior to L'Obscurité's formation, the Kuremisago Family had developed a method akin to that of a ritual that allowed for the way to interact with the Amatsu-Mikaboshi fragment inside of their souls, with the understanding that they could learn to direct its absolutely limitless powers of destruction against their enemies. Of course, with learning to channel this power, the user had to also undergo intense sessions of physical and mental training in order to discipline themselves to be capable of utilizing this strength without being consumed by it.

Klaus Nietzsche stated that the Zanpakutō itself is the physical manifestation of the wielder's heart. Therefore, Mukai is the method of channeling that fragment of the Amatsu-Mikaboshi within the user through their Zanpakutō and unleashing its power which results in a unique transformation.

Notable Users
The only known users of the Mukai are acclaimed to be the nine Ichiken Kyūkage of L'Obscurité and presumably Kurama Kawahiru.

Behind the Scenes
The concepts behind Mukai are based on actual Shinto beliefs, in that upon the destruction of the Amatsu-Mikaboshi, the remains were said to linger and to live on in the hearts of humans, which is said to be the prime reason behind intense emotions in human beings, such as hatred and anger. There was said to exist certain Japanese sorcerers that attempted to establish a cult of worship of the Amatsu-Mikaboshi in the attempt of developing a method of directing its power of destruction against one's enemies through shaman teachings. Ama-no-Kagaseo was said to be the corporal form of the Amatsu-Mikaboshi, having become much closer to a Satan representation by this time, who drew his power from the Pole Star. The idea was that if you let the Amatsu-Mikaboshi feed your passions for greed or lust but then turned to control them through intense discipline, you yourself could harness its power of control and establish dominion over a territory or even the world.