A reference from the PS2 game series "Xenosaga".
U-DO is a strange and mysterious wave existence that is directly connected to the Miltian Conflict and the Zohar. It is unknown whether or not this existence contains any bit of sentience or if it is even a living thing. It is known to produce the Song of Nephilim, which is responsible for turning Realians and Albedo mad. It is also a source of Albedo's power. U-DO is also suspected of the disappearance of Old Miltia, as U-DO surrounds the Old Miltian star system and greatly warps the physics and properties of matter and space.
U-DO is an acronym that stands for the Unus-Mundus Drive Operation system. Dmitri Yuriev, father of the U.R.T.V. units, and others who were studying U-DO told the government that U-DO was an artificial consciousness or A.I. linked to the U.M.N. that was carrying some kind of dangerous waves. That was a complete lie, told in order to hide the fact that U-DO was something Dmitri Yuriev did not entirely understand. U-DO is actually an energy from a higher dimension, an entity humans could not possibly control. It appears as a huge cloud of reddish-colored gas and can create space-time anomalies.
The U.R.T.V.s are specially designed to combat U-DO; they are U-DO's anti-existence. U.R.T.V.s can produce anti-waves designed to resist U-DO, but these anti-waves will not neutralize each other. The waveform collision between these anti-waves will release enormous amounts of thermal energy, resulting in the destruction of anything near them, including the U.R.T.V.s. A moment before the U.R.T.V.s were to destroy U-DO, Rubedo had a vision of the Old Miltian planet being destroyed in an enormous explosion. Rubedo, fearing for the lives of his companions, broke the psychic bond that would produce the anti-waves. Unfortunately, this left them with no protection against U-DO. U-DO slew or drove mad all of the standard U.R.T.V.s. It then infected Albedo and drove him mad as well. The only documented surviving U.R.T.V.s were Nigredo and Rubedo, though Albedo survived as well.
