In this world, the Soul Realm is an exceedingly unique existence.
Unlike Subspace where storage spaces are located, it isn't a physical entity space but rather a conceptual space overlaid atop the spirit world.
Its history traces back to the "Premonition Dreams" of ancient ritualists.
Some wielders of Extraordinary Power among the ritualists claimed they could communicate with deities in their dreams, receiving revelations about the future... These unusual dreams were the early forms of the Soul Realm!
Late in the First Epoch and early in the Second Epoch, after meditation theory had matured, the majority of magicians had mastered the ability to sink their spirits into the "Sea of Consciousness."
This "Sea of Consciousness" was, in fact, the personal equivalent of the "Soul Realm."
Within it, individuals could examine their own spirit, converse with themselves, but couldn't directly establish contact with others or even deities... unless through some medium.