Nullificare (Nullification Arc)

The Nullificare were a species of Spiritual Entity that instead of being aligned - for good or ill - with the Soul King's spiritual energy: "Reiryoku" or "Spirit Energy", they instead use the spiritual energy of the Soul King's to-be over-thrower: "Youki" or "Demonic Energy", the Nullificare exist to Nullify Reiryoku through absorption and corruption while destroying the Spiritual Balance. Very often, the Quincies are their servants and cause destruction in their names, helping them in their goals although they are often unaware of this.

Overview
The Nullificare are unearthly beings living in a world ruled by a different logic than those seen up to the present date, they have an odd Anti-Reiryoku known as Youki and are made up physically of corrupt Reishi known as Dark Matter, they are often invisible to those without Spiritual powers however if they choose to appear before them it usually means in their death.

Nullificare are led by their King Shinen and his Commander-in-Chief is his older sister: Hebi, he has two Councillors are the twins: Zanshi (Violent Death) and Eimin (Eternal Sleep), whom often like to manipulate Hebi against her will while she acts on her brother behalf with his best intentions in mind.

Shinen also has a consort that is sometimes reincarnated as a Shinigami and has Captain-level powers, once corrupted his Zanpakutō seems to disappear and he gains two unique Resurrección, the consort is called Kaosu every two thousand years.

Combat
Nullificare all have roughly Captain or Lieutenant power however not all of them have the capacity to wield this power wisely or effectively, many however not only wield this power both effectively and wisely but also evolve to a Royal Guard's power level, the most powerful however are Shinen, Kaosu, Zanshi, Eimin and Hebi.

Nullificare can absorb the knowledge and power of anyone they choose, literally absorbing the Reiryoku and Reishi that make them up, they also gain the abilities of those they absorb and many of them have absorbed Hollows and Arrancars before allowing them to have the capacity to use Cero and Balla.

Nullificare wear armour that is usually a "Resurrección" and they are believed to be the first users of Resurrección predating the Arrancars, Shinen is one of the few Nullificare to wield a Zanpakutō with an active Bankai form, and to have a Resurrección.

Trivia

 * Nullificare is the Latin word for "Nullification".