Lightfeeder

A Lightfeeder is a type of Pureblood Heartless, those who have consumed too much light. There are only seven of this species, due to there being only seven Princess of Heart. Each Princess has a Lightfeeder that goes after them, consuming the light of their world. Lightfeeders are able to use both the power of both light and darkness to attack, having an equal balance.

Lightfeeders are special due to the fact that they are Heartless who are corrupted by the darkness, but at the same time have light within them, due to their consumption of light. Although Lightfeeders have equal strength, they are more influenced by the darkness, due to the fact that they are indeed Heartless.

Origin
Yen Sid explained that the Lightfeeders emerged after the events of Kingdom Hearts I, when all worlds were restored, and so was the light. Certain Pureblood Heartless started to consume an abnormal amount of light in seven worlds that the Princess of Heart reside in, and they were slowly getting stronger. After the events of Kingdom Hearts II, these Heartless came to the point that they were labeled their own subcategory, having unique characteristics.

Yen Sid's theory was that if they consumed too much light, the world would be destroyed, taken over by too much darkness, resulting in a world's destruction. Soon, the Lightfeeders would travel to other worlds, through the newly created Vents, and destroy one world after another.

List of Lightfeeders
Each Lightfeeder is after a certain Princess of Heart, at a certain world.