Chaos

Ilias: "This, this Is the layer of nothingness...!? The nothingness is materialising and devouring the spaces...! If this spreads further, the whole world will become nothingness... Is that... the 'chaos covering the world' means...? We have to go further. Don`t touch it. If you touch it, the outcome will be the disappearance..."

Sonya: "Oh? It`ll disappear if I touch it?"

Illias: "...of your hand..."

Sonya: "Gah! I`ve almost touched it-!"

-Ilias and Sonya, at the 3rd Tartarus

"It turns out that this world didn`t follow the correct history. Somewhere in this history, the paradox occurred, and it turns every space and the world itself into chaos. Chaos is the nothingness. Both are the same thing. And the most significant paradox it seems originated from this other universe. The paradox from this other universe... it made a chain reaction that affected this world. And the whole parallel universes will collide with each other. Then, the whole of all universes will be devoured by the chaos... and what will be left is complete 'nothingness'."

-La Croix, at the Administrator tower

Chaos, or Nothingness, is the inter-dimensional phenomenon occurring in Monster Girl Quest: Paradox. It began in an unknown parallel universe where the first paradox occurred, and now spreads through all other universes. The Paradox was a result of that world not following the correct history.

The apoptosis phenomenon is an immune mechanism phenomenon of twisted dimensions to make this slow by preventing inter-world interactions, which are fruitless endeavours since the chaos spreads too fast.

Trivia

 * Chaos could be referenced first of the primordials, in Greek mythology. Khaos wasn't so much a living thing, as it was a primaeval state of existence. It was the void itself. Nothing. You can probably see the connection between the Chaos in Paradox and the Khaos in Greek mythology. Outside of the obvious one, Tartarus was also one of the primordials and is a descendant of Khaos. Fitting, when you consider the Tartarus's in Paradox were a result of Chaos seeping into the world.