You've probably seen me use the term "Greater Soulstream" or at least just "soulstream" before in RP, but what the hell does that mean? Let's find out!
At least in terms of the Isoverse:tm:, there's a background radiation of soul energy in the universe, existing in a constant cycle of becoming and dissipating. It's not too different from how atoms drift about, connecting into molecules and then into Things and those things eventually wearing back down, sometimes even to an atomic level. Souls work the same way. If a soul doesn't get reincarnated or head into an afterlife, it just dissolves into space and becomes part of the background magical radiation of the universe: the Greater Soulstream.
The Greater Soulstream is ultimately where all souls come from and from where magic is ultimately drawn. When a deity creates a new soul, it's basically just consolidating a bunch of soul dust. Only the Creator - in our case, Frenzael - has the ability to wholesale introduce new soul energy into Entirety given their nature as literally being the metaphysical concept of creation. This is what makes Lil Strawberry (from Altirety) so notable; Altistra created a new soul for her rather than a "new" soul. Magic, meanwhile, uses the latent soul energy in the universe to make miracles - breaking physics to make shit pop out of nowhere and manipulate elements and what have you - happen.
Of course, how magic works in a given universe can vary, but the Greater Soulstream is ultimately the source. In some worlds magic is drawn from faith in a god, but the god themself is undoubtedly filled with soul energy and unconsciously charged by the Greater Soulstream. Likewise, magic drawn from artifacts or other objects is really drawn from a consolidation of soul energy, magic drawn from one's own soul energy obviously originated from the Greater Soulstream in some way, so on and so forth. When settings have raw magical energy about, it's ultimately just that world's physical manifestation of soul energy, or one specific presentation of it.
While there is nowhere in Entirety untouched by the Greater Soulstream - anywhere it is not is where the borders of Chaos (the void of raw possibility between Entireties) begin - there are places where it is "weaker" or "stronger", hence the presence of "steam". Like water currents, there are places in Entirety where the volume and flow of soul energy are intense, making great and wild magics easier to pull off and heightening their dangers. There are other places where the flow is light, and life is thus sparse. In other places the stream is placid but bountiful, creating "pools" where densely-populated galaxies inevitably arise. Typically this "flow" isn't visible, measurable only by expert soul scientists and magicians greatly in touch with it, but there are exceptions to this rule.
Places where the Greater Soulstream tangibly manifests are called soulstreams - the lesser soulstreams to the Greater Soulstream's... Greater Soulstream. These might manifest like the bands of the Milky Way in a clear night sky, only really visible from afar. Other times they can be ley lines or literal streams running through space or across planets, such as in the case of Holann's bizarre soul ocean. Soulstreams are highly coveted territory by just about everyone: countless wars have been waged over soulstreams by magicians, monsters, demons, deities, and those who fear all of the above. Ironically these wars only fill the soulstream with more soul energy, making it more and more desirable. This can quickly lead to the soulstream "flooding", bringing with it the risk of soul corruption, strange entities arising from the soulstream, magic behaving in unexpected ways, people "eroding" and having their souls swept away, all kinds of fun things!
At times, fully-formed souls can be found floating through soulstreams. These have one of two origins: they may be souls that have just finished coalescing, or they may be the souls of the deceased drawn in by the flow. In the case of the latter, the soul will gradually erode over time if it isn't removed or doesn't find its way into some universe's reincarnation loop, etc. This erosion is the reason why necromancy can often lead to people coming back wrong or not coming back at all: their soul has been worn away at and no longer fits in the body quite right, is missing chunks of memory and personality and qualia. It might not even be there at all, instead just slopping random soul energy inside of a corpse and creating a monster.
In the case of the former, however, the soul will absorb more and more "soul dust" until it's either harvested or becomes "heavy" enough to drop out of the soulstream like a ripened fruit, finding its way into a body or falling into some sort of greater system that directs it elsewhere. If the soulstream is "moving" fast enough to keep the soul from "falling" or if it forms a deep enough "pool" to keep it afloat, the soul will absorb more and more soul energy. This creates a soul of greater and greater power, and it is these souls inevitably become powerful magicians or even deities, with entire universes being born from these puddles in the middle of nowhere where the conditions for a god's birth happened to arise.
One consequence of Entirety's age is that it is now filled with entities advanced enough in technology in magic that they end up seeking out soulstreams for their own gain. This has led Entirety to an age where fewer and fewer gods and souls of immense power are born due to people co-opting soulstreams, fishing up souls and bleeding streams dry before they can ever produce deities. Even if not for the ever-expanding nature of Entirety, though, there would still never stop being gods. As mentioned before, coveting soulstreams eventually leads to wars that lead to much soulshed, wiping the slate clean and allowing a soulstream to produce once more: one of Entirety's many funny little cycles. Still, this does go some way to explaining why primordial deities have a tendency so much more powerful than modern ones even outside of age allowing expertise and wisdom: in addition to the abundance of raw anima mundi and prima materia at the time, Entirety's then-untouched nature allowed soulstreams to nurture immensely juicy souls. Mmmm.