Kūkyo māku

Kūkyo māku refers to the race of individuals 'reborn' with their souls stained by Emptiness.

Overview
Kūkyo māku is a race of individuals whose Souls are stained and fragmented by Emptiness, the antithesis of existence. Essentially they are 'reborn' outside of the equilibrium of souls, and are considered a poison to the equalibrim. While it is possible to reverse the process, it is currently unknown. Anyone whose soul is stained by fragments of Emptiness helps bind the existence of Empty Queen, the first Kūkyo māku and further increase her powers. Anyone who dies while still afflicted by Emptiness will neither reincarnate nor return to the equalibrim and will in fact cease to have ever existed(though their death will have no negative impact on the Empty Queen's existence or powers)

Powers and Capablities
Dense Spiritual Pressure: A Kukyo Maku's spiritual pressure upon their rebirth becomes incredibly dense, signifying that their soul is stained by Emptiness and is therefore granting immunity to ordinary reishi absorption techniques.

Kūkyo shahei(空虚遮蔽, Emptiness Shield): A dense spiritual energy armor materializes, further increasing defensive capable far beyond what normal Blut or Hierro could provide. In some cases, the defensive powers are further increased rather than gain the spiritual energy that accompanies the form, as in Tazuma's case.
 * Hi Ningen Kukyo: A technique exclusive to Chireru Amakuni, the defensive powers of Kūkyo shahei are converted to his fists, turning it into an offensive power that augments his physical strength considerably. Hi ningen Kukyo and Kukyo shahei cannot be used at the same time, as they are one and the same technique used in a different variation.

Vacío Cero (Emptiness Cero): A Cero exclusive to Hollows and Arrancars of the Kukyo Maku, or other Hollow/Arrancar sporting the same affliction. It is a double layered cero, mixed with a Hollow or Arrancar's original reishi (characterized by its original hue) and their now denser reishi (characterized by its pure white energy). While sporting the destructive potential of ordinary Cero, the second layer can pierce through spiritual defenses like Kido, Hierro, Blut or Kūkyo shahei.

Inyección de Vacío (Injection of Emptiness): The capacity to ultimately inject 'Emptiness' unto others without the incentive to reveal either a Museigen nota jōtai state or another release state, entirely at one's own discretion. This technique originated from Kūkyo no Joō.

Revelación de Vacío (Revelation of Emptiness): By making physical contact, one can force an individuals' Museigen nota jōtai powers to the surface (or even deactivate said powers) upon his/her own whim even against that person's will. The individual in question must have a soul stained by 'emptiness' to begin with.

Museigen nota jotai
For Humans and Quincies, the form it takes is dependent on the reason their soul is stained in the first place( though it is possible for certain Shinigami to utilize this form like this). However, for Shinigami, Arrancars and Kaiju-Ningen, it "melds" with their respective releases, creating inverse, mutated variations of their releases. Initially, the form is accessed by intense negative emotion (for Chireru, despair is required for his unconscious "Museigun nota jotai"),though the form itself is characterized only through the individual's eye's and not in its "true" form, though this is dangerous because they can "inject" emptiness unto another individual if left unchecked, potentially staining their soul as well.
 * True Museigen nota jotai: Those who gain a foothold on their inner emptiness can access their Museigen nota jōtai forms. This form is unique for Shinigami and Arrancar in that it merges with their respective Bankai or Resurrecion when mastered( in Natsu's case, it fused with her Teiki-teki kemono no katachi (定期的獣の形, Recurring Beast Form), though such a fusion is optional and the original Bankai/Resurrecion can still be accessed. however, the form is hard to mantain. Using the form anylonger than 15 minutes runs the risk of an automatic Soul Suicide, depending on one's endurance. Access to this form allows for:
 * Enhanced Spiritual Pressure: This form is capable of a massive increase of potential spiritual pressure, as well as it becoming denser than in an average state.
 * Enhanced Kūkyo shahei: A dense spiritual energy armor materializes, further increasing defensive capable far beyond what normal Blut or Hierro could provide. In some cases, the defensive powers are further increased rather than gain the spiritual energy that accompanies the form, as in Tazuma's case.
 * Kami Museigen nota jotai: A True Museigen nota Jotai form that can be accessed by a true Kukyo no Maku, such as the Empty Queen. Argus observes that Chireru Amakuni has the capacity to reach this form, though is far from attaining such power.