Post-modern World Primitive World

In the future in 2020:
It was a dark peaceful night when a meteorite fell into the earth carrying an unknown carbon compound. When the asteroid reached the Earth's atmosphere, a series of explosion occurs and the carbon compound fuse with every element or compound it had contact with. Unstable fusion and fission occured, gasses that pass through the human body sometimes fuse creating an abomination or it could fission, which cause the body to explode or deconstruct. Some animals deconstruct creating a vile of liquid, when taken in cause transmutation or transformation into new creature or prehistoric creature. Human and animals become cannibals. Evolution goes reverse and earn new characteristics. Animal instincts went wild, panic surge throughout the whole world. The END of the World.

At least that's the prologue of Rei's story.