Reigai

A is an artificial and spiritual body that allows artificial souls to maintain a physical form in the Soul Society.

Overview
Artificial souls have no physical form in the Soul Society in the same way that they don’t in the Human World. While in the Human World, they can be placed in a Gigai or other forms of bodies in order for them to interact with the environment around them. In the same way, they can be placed inside Reigai while in the Soul Society which allows them to interact with the world there. In this capacity, they are used for experiments conducted by the Shinigami Research and Development Institute in the continued development of artificial souls that are used by Shinigami during missions to the Human World.

Reigai can also be designed as a nearly perfect clone of a real soul that maintains the memories, personalities and thoughts of the original soul the body was cloned from. In this capacity they can be used to infiltrate certain groups while being controlled by an outside source, even against their will. Despite being perfect clones of their Shinigami counterparts, they are shown to be incessantly more violent, a characteristic which increases innumerably during a battle. Also, even though they have the same abilities, Inaba modified them so that their abilities far outclassed those of the original Shinigami. For example, the Reigai counterpart of Marechiyo Ōmaeda wielded a much larger version of his Zanpakutō, and Izuru Kira's Zanpakutō increases weight ten fold instead of double.

Reigai are also shown to emanate a purplish spark from their eyes, which happens at regular intervals. A subsequent glow remains present, giving their eyes a purple tint. The Reigai also carry with them an unusual bracelet on their forearm, although the purpose of this object is currently unknown.