Darkness

Darkness is a parallel force to Light in the Kingdom Hearts universe and is also a form of attack from the Kingdom Hearts games. Darkness is commonly associated with evil due to it being naturally deceptive and misleading. Because of its corrupting power, people can lose their hearts to it, becoming "Heartless". Those that follow the path of darkness (villains such as Maleficent and Xehanort's Heartless) gain enormous power but usually lose much of their physical selves to it. Riku's Keyblade represents darkness though he personally follows the path of light.

Darkness can apparently be used for more then just a means of attack and transportation, as it can also alter the appearance of the user. Ansem and Riku are two of the users of darkness that can change appearance using darkness, Riku used it to transform into Xehanort, while Ansem used it to take his appearance as DiZ, as well as transforming into Xehanort like Riku.

The Dark element is also used as a form of attack by the Heartless, Nobodies, Riku, and some bosses, but not used by Sora, nor his party, except for Riku. Sora and his party may be protected from Darkness attacks by equipping items such as the Midnight Anklet.