Dark Matter (Nullification Arc)

Dark Matter (Dākumatā) is the corrupt equivalent of Reishi and the very essence that makes up the Nullificare and alters their followers over time, Dark Matter can destroy anything made of Reishi and rumors of a weapon designed to pierce the Sekkiseki Walls around the Seireitei appear every two millennium, causing mass panic and fear which in turn lead to more potential recruits for the Nullificare.

Trivia

 * Dark Matter is often considered to be the opposite of matter, therefore capable of unknown feats, sometimes found in the destructive energies of a Black hole.