The Shadow Vortex is a mentioned concept in Shin Megami Tensei III: Nocturne.
The Shadow Vortex is the logical offshoot of a world which has failed to force the beginning of a Conception, and has thus let its energy run out. This causes the entire timeline to die as all energy in the universe is exhausted. The collection of dead timelines is called the Shadow Vortex, where the gods indigenous to these, now powerless, become entities known as false gods; in an attempt to restore their existence and power, they flee to worlds experiencing the Conception and try to acquire enough of the power of the new reality to become part of it, essentially becoming "real" for that timeline. Aradia was one of said gods.
However, the existence of these false gods is forbidden in the Conception, and they must find ways of forcing their will without contravening the laws governing the entire process of death and renewal.