Fall (DTD)

The Fall is the process by which an angel severs its connection to the God-Machine and becomes one of the Unchained.

Angels can Fall for many reasons, and the direct causes of a Fall are often complex. However, in general, the Fall is the result of a desire for autonomy from the God-Machine. The process is intensely painful and overwhelming, as the Unchained merge with their Cover and gain Primum. The newly-made demon loses most of its angelic powers, including the ability to use Numina and manipulate Essence; it must now learn to harvest Aether and use Embeds and Exploits. It may also have lost elements of its memory and angelic identity.

When a demon Falls, there is a noticeable effect on world around it. Stigmatics are usually aware of a nearby Fall and may be able to track down the demon.

The Fall is always the result of a conscious choice to reject the God-Machine, even for Integrators. Angels who lose their connection to the God-Machine without undergoing the Fall are Exiles.

Reference

 * DTD: Demon: The Descent Rulebook.