The Dark is formless and invisible. It invades the body like a plague, an unseen visitor. Yet those it taints become... undying.
The Dark is a force central to Vagrant Story, being a negative force that exists in the world of Valendia. It is an invisible entity that permeates various places, and helps manifest supernatural phenomena. It is unknown how The Dark came to exist, but it is mentioned that the existence of Leá Monde, the abandoned city of evil, as the Gran Grimoire with its numerous incantations in its walls, came to help manifest and create a "Wellspring" of The Dark.
Regarded as a negative energy not meant to exist, The Dark's influence on living beings varies. Those that remain in its influence awaken latent powers gaining the ability to use magic, such as casting spells and summoning monsters, to awakening psychic powers and abilities on the spiritual level. Those who enter Leá Monde gain new powers over the Dark, such as Ashley Riot's acquiring of magical powers and Callo Merlose's awakening into a Heart-Seer.
Other examples are shown by Sydney Losstarot, such as the ability to cloak oneself in the guise of another person, powers of levitation, and immunity through immortality. As one bathes longer in The Dark's presence, letting its influence grow deeper, they grow stronger in its usage and control. One side effect of being weaker in The Dark's powers and utilizing a feat without much Dark power will have that person be killed or almost die in the attempt.
Users of The Dark are cursed. According to the Vagrant Story Ultimania, souls stained with The Dark are taken out of the natural cycle of life, are not allowed into the afterlife, and are to become one with its collective of other cursed souls, placed into a twisted version of immortality known as "incomplete death". In incomplete death those tainted by The Dark either dissipate into light particles or disintegrate into black dust. Souls stained by The Dark are forced to roam the mortal world driven to madness and harboring jealousy toward the living, and seeking the flesh of those not stained by The Dark to inhabit their bodies to live again.
Another, crueler form of incomplete death, occurs when one dies in a place where The Dark runs heavy, whereupon their soul is not being allowed into the afterlife, but soon comes back to inhabit their recently killed corpse, reanimating as an undead. The collective souls of The Dark come to taunt and drive the person insane to gain the person's corpse, and to kill others to add to the collective of Dark stained souls and have more corpses to inhabit.
Jan Rosencrantz claims immunity to the Dark's powers, likely due to VKP brainwashing according to the Ultimania, but overrates his own abilities. Sydney puts him in his place once properly pushed.
Whoever can control Leá Monde's power will gain immense strength. Romeo Guildenstern and his Crimson Blades undergo training outside of Leá Monde to obtain power over the Dark. Even without the Blood-Sin required to take Leá Monde, Guildenstern is equally powerful as Sydney.
- The phenomena of dying among those bathed in The Dark's powers are mentioned and shown differently among installments of Vagrant Story; in game, the dead dissipate into light particles, while the Ultimania describes death by collapsing into black dust. As mentioned of how the Vagrant Story development saw hardware limitations on the PlayStation, it is likely that disintegration is the canon occurrence.
- The in-game metal, Damascus, is said to be the result of vaporizing metal and reinforcing its structure and consistency by layering it with The Dark, which gives it its dense and tensile characteristics.
- The Dark is referenced in Final Fantasy Tactics A2: Grimoire of the Rift through the Geomancer's ability, Mist Storm, as it inflicts Dark based damage. This in turn shows a connection between The Dark and Mist, both being a source of magic in the world of Ivalice.
- There's a reference to The Dark in Final Fantasy Tactics: The War of the Lions, where Valmafra Lenande's job Witch of the Coven's description states: A witch who has made a pact with the Dark, placing its powers in her thrall.
- Furthermore, the Final Fantasy Tactics secret boss Elidibs features a job command called "The Dark".
- Although seemingly random, there appears to be a subtle link to The Dark and liquor, as names of commonly found weapons throughout the city of Lea Monde bear the names of alcoholic drinks. One notable weapon, Pussyfoot, wielded by Jan Rozencrantz, is a weapon named after a barmade nonalcoholic cocktail.