A Cover is a human identity used by the Unchained. Much more than a simple human disguise, when she first Falls a demon's Cover is the remnants of the Infrastructure that supported her as an angel. A Cover is much more than a backstory and a few props, though. When she Fell, the demon interfaced with reality rather than the God-Machine and wrote her disguise into the world.
Description & Function
Demons have entirely human bodies, fully-detailed backgrounds, relationships, possessions, jobs-whatever was needed for their Cover. The people "related" to the demon don't realize that anything's wrong. In some cases, they did't even exist until he Fell.
Cover can be damaged if a demon deviates too sharply from his human life. The most powerful demonic magical abilities shake Cover, risking exposure. As a demon grows in power, becoming more connected to the universe, her Cover may develop glitches-obviously inhuman traits, like metallic skin or a need to drink mercury, strange emanations of power such as damping radio signals, or bizarre behavioral tics and compulsions like a need to remove the eyes from photographs in case the God-Machine sees her through them.
Cover can be replaced. Demons can learn to steal the Infrastructure of angels or take a human soul and "move into" the life it vacated. Demons grow to the point that they can maintain more than one Cover simultaneously, switching between disguises. If Cover is stripped away entirely, the demon has to run. Trapped in his true form, desperate to find a new Cover he can move into, the fugitive has to face groups of angels attempting to capture him before he can go to ground once more.