The Darkening (黒化 Kokuka ) is a terminology used in the Corpse Party series. It is what happens when someone loses all hope and succumbs to their negative emotions - hatred, grief, sadness, envy, jealousy, etc. It causes the victims to act on their emotions, and sometimes becomes completely apathetic and may lead them unconsciously killing others. In other cases, the victims' obsession towards something may also cause them to experience the Darkening.
When the victims regain control of their body after a darkening experience, they will not able to recall any memory of their actions that have occurred during their darkening, let alone realize they were experiencing it.
The darkening will also leave their mind and body vulnerable to possession by malignant spirits. Such as the case of the ghosts; a glance into their eyes invokes this instantaneously.
Darkening manifests on people in different ways, The most common is black mist surrounding their body. However, it can also manifests in other forms, such as black, tar-like liquid pouring out of the body. When the victims are able to fight their darker emotions, the darkening will leave their body, and the black mist surrounding them will vanish.