Origin of Void's Children

On a base level, the dimension that Atovis is located in has multiple planes. Atovis the planet is on the material plane--it has space and time. The two other planes of note, then, would be the supernatural plane--more easily understood as the plane containing magic--and the immaterial plane. All three planes are separate from each other, though the supernatural plane is much closer to the material plane than the immaterial plane is, and occasionally can be reached in some places and with enough willpower and knowledge.

The immaterial plane is a bit trickier to explain. For a high-level overview, we can say this: it has no time or space, and contains an innumerable amount of consciousnesses. These are what the inhabitants call void's children. Void's children have existed for a non-measurable amount of time, possibly since the birth of the universe, and while on the immaterial plane, exist in a hive-mind-like stasis. They communicate without barrier, have no mortal body, and are able to spectate the material plane without the concept of time. They have no government or feuds--they just exist.

In an odd and largely inexplicable event, the three planes were jostled from their regular positions and collided for a brief amount of time. This resulted in a number of occurrences:

One: A large amount of magic from the supernatural plane entered the material plane

Two: Many (or, possibly, all) of the void's children were bumped from the immaterial plane to the material plane

The nearly simultaneous positioning of these two events collided in an interesting way--all void's children in the material plane spontaneously formed bodies, loosely based off of the pre-existing inhabitants of Atovis. The reason for this is largely unclear. Nearly all of the bodies spontaneously generated for the void's children have odd characteristics as side effects of the magic, ranging from being largely unnoticeable and inconsequential to the body being sustained completely off of residual magic. In a number of cases, multiple void's children found that they were placed into the same body--similarly to people with dissociative disorders such as DID. Their plurality exists in a similar state to DID, with different individuals in the system being able to front, co-front, or do things inside a headspace. 

The new presence of strong magic has also urged many to participate in witchcraft and wizardry, of a sort (those who practice magic are not often inclined to call themselves that, though there is the occasional self-proclaimed witch or wizard). This is seen as an odd and often dangerous past time, as well as uncommon, but it's not unheard of. While there were small numbers of magic practicers already in existence in places where the supernatural plane was closer to the physical plane, it was seen as a religious sort of thing--practicers gathered in convents and small communities in relatively magic-rich areas to experiment and learn from each other, many of which were rather remote and cut off. Now, you can find small groups of magic practicers all over Atovis, especially in large cities. Some void's children seek to use magic as a way to mask their other-ness, and often find they have a knack for practicing.