Hallownestian Void

"Souls, shadows of souls, lost memories, psychic imprints, tragedy and regret all powerfully mixed."

Hallownestian Void, more commonly known simply as Void, is a substance, a force, an entity and a collection of entities all in one.
Originating in the dream of Hallownest, Void appears under bright light to simply be a dull black liquid, sometimes emanating dark gas. When not under such light, it reveals more of its true nature: It roils and writhes, generating lashing tendrils and glowing white eyes across its surface.
In truth, the Void is a sea of souls and nightmares. It is simultaneously the nightmare emanation of the souls within it, the substance of those souls, and the thing controlling those souls. It is the contents and the substrate that contains the contents. To make matters stranger, not all of the 'souls' in the Void come from the dead. Some are concepts, emotions, or memories striving to be self aware. Most of these feelings tend to be negative or dark, but not all are.
Despite the nature of its component parts, in practice Void's most prominent characteristic (and the origin of its name) is its apparent emptiness. It has little mass for its volume, and in many cases it seems to be bigger on the inside, capable of consuming, storing, and preserving objects far in excess of its apparent size. It naturally collects and assimilates loose souls. It is, in many ways, an all-consuming void. It is well, then, that it is lacking in direction, mobility, and any sort of coherent focus.

Void Constructs

During the time of the Black Hive and throughout the later days of the Pale King's kingdom of Hallownest, constructs and beings were formed from the substance of the Void for a variety of purposes. The Black Hive made Void ants as mindless servants and laborers, much to the (unnoticed) displeasure of the Void itself. The Pale King experimented with Void-based guards and sentry drones. And as Hallownest fell, the Pale King created the most powerful and long-lasting of the known Void creations, the Vessels, the result of the drowning of the Pale King and White Lady's unhatched eggs in the substance of the Void. A number of Vessels survive to this day.

The Void Heart

An emptiness that was hidden within, now unconstrained. Unifies the void under the bearer's will.

The Void Heart is a charm permanently merged with Knight, the greatest of the surviving Vessels and the one who finally fulfilled their purpose. The charm is a birthright reclaimed, a signifier that its bearer is both of the Void, and master of it. In practice, this primarily means that the Void will not harm Knight or work against them, but it has also unlocked paths to power over or unity with the Void that would otherwise be dangerous or impossible, and the Void and its shades have rallied against Knight's enemies more than once.

Void Magic

Various methods have been found to use the Void as a source or vector for magical power. Knight pioneered Void-augmented SOUL spells, screaming blasts of life energy and darkness, and is evidently the source of their power. The queens of the Black Hive mastered a skillset that made them "Void shapers", able to force the Void into constructs that served their whims. A book retrieved from Cubit named Voices of the Void gave instructions for the Voidmage variant of magecraft, a skillset that would lay the foundation for the future Voidmage Academy and the education of Et-Kehri. It has even been hypothesized that Knight could act as a patron to warlocks, granting them the power of the Void.
In all cases, Void magic tends to be disconcerting in appearance and side effects. Screaming ghosts, eldritch whispers, black tentacles, and far too many eyes are expected quirks or manifestations of spells. However, scary does not mean evil. Thanks to the influence of Knight and Ngel Sfet, the vast majority of Void-based spellcasters are Neutral-aligned at worst, and most are benevolent adventurers, researchers, or defenders of their communities.

Type

Metaphysical

Color

Void black

Density

Surprisingly low

Common State

Liquid