Ages ago, God wanted to know which side would win in a war - good or evil. To find out, he created the world known as Atmos.
For centuries the demonic Akuma waged a war against the heroic and pure Angels. The battles were massive in scale and horrific - the angels were slaughtered in droves, God simply watching as the chaos grew and fire ravaged the land. The monstrous Akuma devoured and destroyed everything they saw.
The Archangel Kraus was mortified by what he saw. He begged God to allow him and the six other Archangels to intervene and bring the war to an end. His pleading was in vain, as God refused to let Kraus end the war. After centuries of attempting to reason with God and witnessing the destruction of his world, Kraus eventually had enough. Gathering three hundred of his most loyal Angels, Kraus tore a hole in the fabric of Atmos and created the world of Eternia.
After creating Eternia, Kraus sealed off all contact with Atmos. Atmos' current state is unknown.