The place they were in was commonly referred to as the high-level battlefield by the combatants and the military personnel. And it wasn't without reason. It was a high-level plane, after all. And it was one that should be able to withstand the battles that broke out on it, so it was of decent quality as well, which meant that the plane's natural mana levels should be quite good.
After the war broke out, numerous combatants had entered the battlefield and fired off magic and aura with their mana before dying and letting all the mana in their bodies escape into the air. If the mana on the plane exceeded the plane's capacity to retain it, the mana would leak into the Void.
