Kiheitai

The Kiheitai (鬼兵隊, "Army of Demon Soldiers") is a group of Rukongai citizens that were collected by the Quasso Regios over the course of two thousand years, each imbued with a specific Kidō by Miyatsu Asakura that serves as the core of their individual powers.

Organization Overview
Within the Kiheitai, there are an indeterminate number of souls that have each been imbued with a particular Kidō spell that fit their nature and personality so as to maximize the spell's effectiveness in their hands. Following this, they were trained by Miyatsu to harness the spell's power and turn it into their own skill. However, it was noted that some subjects were not able to handle this integration of the spell and their soul tore apart at the seams.

History
Despite the vast collective military power of L'Obscurité, Kurama Kawahiru ordered Miyatsu to gather souls that could be used as expendable soldiers in confrontation as well as to compensate for any possible unforeseen situation. Furthermore, he felt it wise to possess a military force that would be under his direct command should any Ichiken Kyūkage attempt a coup. Over the course of two thousand years, the Quasso Regios members were tasked in gathering citizens from outer Rukongai districts that bore a strong hate for the Gotei 13's "cruelty". They were eventually turned into the ranks of the Kiheitai.