Nexus

The nexus is the birthplace of all soulless, and is the space between each multiverse. entering this void is considered suicide due to the immensity of the soulless in the realm, and tha fact that this realm is where the Destroyer is destined to be born in 2012

The Nexus is mentioned in 15 Keys and is only seen again in 15 Keys 4, where Zach, Kristine, Hopey and the other chosen enter it to save the world, it is revealed that the Hooded figure and other characters from Fate by Blades have already entered the Nexus and are under attack by the soulless.

The nexus is the darkest place imaginable, in the fact that you will be trapped in there with the strongest soulless ever to exist. In time this would wear you down and you would be consumed. It is confirmed that the hooded figure became the entity he is in Fate of Blades by entering the Nexus at 16 when he was near death. it is unknown what ressurected him but it gave him amplified powers in the fact that he can "Do whatever the fuck he wants."

The Nexus is the third known location in the multiverse.