One of the many alternate dimensions (or "Realms") connected by Nihilitree

Half of the world is extremely cold at all times, despite being permanently illuminated by the sun
Half of the world is extremely hot at all times, despite never facing a star or natural light from space

Fantasy

The Earth's rotation had been slowly changing for centuries, and there was now one side that always faced the sun with one side that never saw daylight
The side that faced endless light faced very dangerous levels of heat and radiation while the dark side was too cold for life to exist
Then a brilliant scientist by the name of Silas Frostspark came across the Gift
They came up with a way to create a source of coldness for the sunny side and a way to warm the other using it
He then sent his two older siblings to place the devices on opposite sides of the planet, hoping they survive the journey
It's unknown how the siblings actually did survive, but they ended up placing the devices in their respective locations and activating them
Unfortunately, Silas had severely miscalculated the immense power held by the Gift and the devices changed the world in an unexpected way
From the dark side of Earth, an intense heat wave started rapidly spreading across the globe
From the bright side of Earth, an equally intense burst of cold started covering the planet
These two powers collided at the halfway point, making the transition from one side to the other an extreme and sudden change in temperature
After a few very tough years, the entirety of the human race had adapted to one side or the other
The two who originally traveled to place the devices became King (Glacier Frost) and Queen (Ember Spark) of their sides, strangely gaining new names along with their titles
Nobody seemed to mind though, as these new leaders helped with adapting to the harsh conditions everyone was placed in

[More will probably be added]

Silas used Riftmaster's Gift to create the Flame Core and Frost Core, which changed the world upon activation

The same as ours

The Rulers of the Realm can draw upon the Power of their Cores (Glacier Frost with the Frost Core, Ember Spark with the Flame Core)
Other than that, Magic does not occur naturally here

No technology, as the extreme temperatures ruin all electronic devices

The Change takes place in 8479 CE

The theme of Fire and Ice, mainly