In the Thirteenth Universe, in the galaxy designated as Galaxy GO619 is a planet known as Ko. The planet is tidally locked to its star but because of the fact that it has four moons it experiences climates, seasons and tides.
But this doesn't mean every part of the planet is habitable. The centre of the side which faces the sun is too hot to support normal life so only very powerful beings can go there.
The opposite side of the planet, The Darkside, experiences the opposite of what the Lightside experiences. The centre is so cold that only the most powerful beings can reach there.
Life thrives on the edges of both sides and the inhabitants of the Lightside have evolved to need less or no sleep.
Since life on the Darkside is harsher, the beings on the Darkside evolved into very powerful creatures compared to those on the Lightside.
Occasionally, powerful creatures from the Darkside would flood the Lightside and kill as many creatures of the Lightside as they like.