The Plains of Bone is a massive soul reservoir, where souls are buried like mineral deposits, and the Soul Pool is a unique mining tool.
This is the only way to explain why the Skeleton Soldiers in the Plains of Bone seem endless, like repeatedly harvested chives.
This mirrors the endless cycle of the Bottomless Abyss and The Nine Hells, serving both as a prison and a place of suffering for those souls, where they endure limitless cycles until their last trace of will and memory are worn away to nothing.
On the Material Plane, falling into the Abyss or Hell is a vicious curse, a punishment Khan Yamun intended for Gaven.
But things turned out differently.
Gaven's ability to stir things up far exceeded Khan Yamun's expectations. Not only could he thrive in The Eastern Desolation, but also cause significant waves in the Bottomless Abyss or The Nine Hells.
Meanwhile, Gaven keenly noticed hidden information.
Under the same domain, the Soul Fire is not infinite.
