U-DO is a powerful metaphysical entity, short for Unus-Mundus Drive Operation.

It is a wave existence that dwells in the higher Upper Domain, capable of observing mankind in the Lower Domain through terminals. It is through this observation that U-DO's power can be accessed.

U-DO is closely linked to Zohar. For most, direct contact with U-DO strikes humans with a powerful fear. Humans who come into contact with U-DO may see the end of all existence, as well as fears of absolute loneliness.