heartless

The Heartless (ハートレス, Hātoresu?) are physical, living manifestations of the darkness within people's hearts. They manifest in two forms; "Pureblood" and "Emblem" (Emblem Heartless being created artificially), and they behave entirely devoid of emotion, hence the name "Heartless".
As Xehanort had yet to release the Heartless in earnest, very few Heartless appear during Terra, Ventus, and Aqua's adventure. When Ventus had still been Master Xehanort's apprentice, Xehanort had summoned several Neoshadows in order to force the boy to embrace his darkness, but Ventus refused, and was soundly...

The Heartless reside wherever darkness is abundant, especially the Realm of Darkness. However, they also reside in places such as the End of the World, a collection of the remnants of worlds that is located near the darkness. Another area that the Heartless live in is The World That Never Was, the world of the Nobodies that rests dangerously close to the darkness upon which the Heartless thrive.

Heartless, as they seek and consume hearts, also desire to return to the greatest heart, the cœur, coeur of all worlds, Kingdom Hearts, that resides deep within the Realm of Darkness. And because of this,...

While the Heartless were not researched with the intent of creating a fighting force, their very nature as manifestations of the destructive force of darkness made them naturally suited for conquering and destroying the various worlds. Their natural ability to travel to various worlds through the use of Corridors of Darkness makes it virtually impossible to fully defend a world from Heartless, and the method in which they are created and exist make it practically impossible to cut them off at the source. Even fighting them once they appear is made difficult due to their immunity to standard...

According to legend, the people of the universe once lived in harmony on one world, with their hearts full of light. Unfortunately, they began to selfishly fight over the light, and darkness grew within their hearts, covering everything and destroying the world. The light survived in the hearts of children, who were able to rebuild the broken fragments of the one world into many, smaller worlds. However, the true light was still hidden in the darkness, so the worlds remained separate.[2] As manifestations of that Darkness, natural Heartless have existed within the Realm of Darkness ever since....