Darkness (UXC)

Darkness is a character in Kingdom Hearts Union χ. Its true identity and purpose are unknown.

Kingdom Hearts Union χ
After being defeated yet again by Prince Phillip and a Keyblade wielder, Maleficent retreats, frustrated that she cannot win, and runs into a mysterious figure calling itself as Darkness. The figure explains that the Master of Masters knew Maleficent would attempt to change her past by travelling through time, and that as a result, the Enchanted Dominion she had travelled to was actually created as unalterable data. Although the world is a trap to prevent her from changing the future, Darkness explains that there's a way for her to return to her own world.

Darkness leads Maleficent to Daybreak Town, explaining the key to returning to her time is in the world. Together, they make their way inside the clock tower, and Darkness explains that Maleficent will find an incomplete lifeboat in the real Daybreak Town clock tower which will aide her in returning to her time. When Maleficent questions Darkness's claims, Darkness reveals that according to the Book of Prophecies, Maleficent exists in the future.

Kingdom Hearts III Re Mind
Sora begins to journey through the hearts of the guardians of light in order to rescue Kairi and enters Ventus's heart. Sora attempts to call out to him, but a mysterious voice tells him that Ven is too pure, and therefore reckless. When Sora questions the voice, it introduces itself as "Darkness". Sora, confused, calls the voice Vanitas, but it instead transforms into the Dark Inferno χ Heartless and challenges Sora.