Every action creates an equal and opposite reaction. Whether that action be physical or metaphysical had absolutely nothing to do with it. The reaction will be there, we just weren't ready for it.

In the year 1223, we did it. We created the first Subshadow human. Subshadow is a thing with matter that doesn't cast a shadow. They are above/ below human, making them able to perform feats that humans cannot dream of.
Magic?

Who knew that beings without shadows would spawn shadows without beings?

In the year 1225, after countless subshadow humans were created for varying reasons, mainly military, the antishadows found us.

Every action has an equal and opposite reaction. I fear that this reaction will destroy the world.