Got permission from planck to comment, anyway I'm gonna try to explain why it's conceptal and then eat and sleep.
Souls
Souls are the metaphysical nature and form of beings, shaping the physical objects they possess after them. As we know, Souls are made up of a beings form, but as to what this "form" encompasses has been poorly explained by our pages, fortunately, the Games have shown context to what this form actually is.
Souls are the metaphysical nature and form of beings.
We see this instance as it's most obvious when Kratos and Atrues battle the immortal wolf Garm,
whom doesn't possess the nature of dying due to lacking a soul.
The father-son duo try to overcome this
by inputting a soul within Garm, Which causes a
change in his nature to be replaced
by Fenrir's.
This is the most obvious one, But their are other instances,
Such as a God's nature battling what the mind perceived as it's nature as said by Mimir and
Freya, But those would take a lengthy time to explain their nuance.
The conclusion here is pretty obvious, Souls are the metaphysical form and nature of a being, And when put into a body they override it's nature with its own.
Beings mold themselves after their soul.
This one is the most obvious one, As the games hammers this pretty clearly.
As mentioned before hand, Having Fenrir's soul put in Garm caused Garm to
have Fenrir's eye color and fur.
When a Giant's soul was put in a soulless snake (I'm sorry you're gonna have to watch a bit of beginning), It caused the snake to
grow as a Giant and even become one on a physical level, As the snake here is Jomungander, who is noted to be a Giant.
Even
the Greek saga had it has a thing, Showcasing this as being a inherent property of Souls.
Souls predate time and space.
To go over this, Magic, a conceptal force on its own, something synonymous with the soul,
is older than the entirety of the Nine Realms and existed in the Ginnungagap as a primordial essence
Ancients, a race of primordial stone who existed as a part of Ymir,
have Souls.
The Light of Alfheim is a power that existed
before the creation of the Nine Realms (Even before Odin) and has gathered souls towards it
since the beginning of creation.
The conclusion here is simple, Souls predate space and time and are thus independent as far as their nature goes.
Primordials And Magic
How does a God's domain work?
A God's
relationship with their domain is metaphysical in essence, ruling
over its nature across
space and time and gaining
magical powers to influence it as a result.
They also have this nature as an aspect of their soul (form in particular) and it is the determining factor between a god and demigod Soul's.
This is pretty obviously conceptal, but how does this relate to the Primordials?
Primordials are their domains and more.
Before we start, I should mention that the Primordials are treated as Gods in the series, so I'll be assuming a God's domain is similar to a Primordial's (the Gods inherited theirs from the Primordials so they'll be similar regardless). Which is why the above existed in the first place.
The Primordials are noted to be their domains and to be synonymous with them,
As shown by how Gaia is said to be the formless sprit of the earth, And how all the Primordials are
synonymous with theirs.
But this isn't all, As all things relating to their domains are created by them, even before time,
As Shown by how
Chaos's Primordial flame birthed all others,
And this isn't something limited to the Greek saga either, As the Primordial flame had created Surtr and Musphlhime,
whom became the source of all flame at the start of creation.
TL;DR
- Souls are the metaphysical nature and form of beings.
- Beings are shaped by their souls.
- Gods rule over the nature of their domains, and have it as a part of their Souls.
- Primordials are their domains.