Hollow

The Hollow are a new kind of enemy first introduced in Kingdom Hearts Oblivion. The Hollow are composed of the Something, and a human body. Due to the Something inhabiting the body of the human, the body now appears twisted and monster-esque.

The Hollow are so named because at first glance, they appear to be monsters with absolutely nothing on the inside. No heart, no soul, not even any Light or Darkness. However, they do in fact have Something inside of them, and it is the Something that acts as the force driving the body to go on. Without the Something in it, the Hollow would simply be a lifeless body.

Creation
The Hollow are created when a person's heart is totally devoid of both Light and Darkness. When this happens, a new essence named Something is able to manifest within the heart. Within a few days, the Something would begin 'eating away' at the person's heart, causing frequent heart attacks and seizures to the person. Eventually, there will be no more heart, and the Something begins to inhabit the body of the person. During this time, the person will become emotionless, and all pain will cease. The person will also constantly lose consciousness and become unable to move their body. Eventually, the Something will attain full control of the person's body, expelling the person's Will and Mind from the body. Then, the Something will warp the body into a monstrous form, and so, a Hollow is born.