The Darkness, also known in-game as the Destructive Force, is a mysterious, incomprehensible force of evil. It is omnipresent, existing everywhere, and represents chaos, death, decay, and destruction, among other similar aspects. It can be commonly seen in the form of the great black sea that exists below the World Pillar. It is gradually sucking the World Pillar into its black hole, and will eventually engulf the entire world, Eto included.
In Gravity Rush 2, it serves as the game's true final boss. It speaks to King Cai in his mind, beckoning him down the path of darkness and convincing him to release Elektricitie from her crystalline prison, so that she might destroy the world below. After Elektricitie's defeat, it makes itself manifest and possesses Cai directly, merging him and his Guardian Wolp into a giant demon. This being can manipulate gravity, being able to remove various aspects of Kat's shifting ability and even remove it altogether.
It offers to allow Kat to survive the oncoming apocalypse in exchange for allowing the destruction to continue, saying that the end of the world is fated and inevitable. However, Kat refuses and manages to defeat it, ending Cai's threat to Hekseville.
However, according to Bit, the Darkness can never truly be destroyed, only sealed away by becoming the singularity within the black hole. Kat attempts to do this, and it is unknown whether she succeeds.