This chapter goes fully into the commentary of humanity's collective unconscious. Or maybe even into the Human Condition (
https://en.wikipedia.org/wiki/Human_condition). It was foreshadowed when Shinra went back in time to the world before the cataclysm. These pictures of 3d Sumire are a flashback to the previous world.
The previous world was basically our normal 3d world. Then the cataclysm hit and the new world was made to reflect the collective unconscious (or meme) of the previous one. The new one lost a dimension. It became a 2d parody full of superhumans.
This cataclysm will erase one more dimension and essentially destroy humanity.