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.