Sanguinary Animism (V:tM Revised, p. 224)
"This derangement is unique to the Kindred, a response to vampires' deep-seated guilt regarding the act of feedingon the blood of mortals. Kindred with this derangement that they do not merely consume victims' blood, but their souls as well, which are then made a part of the vampire's consciousness. In the hours after feeding, the vampire hears the voice of their victim inside their head and feels a tirade of 'memories' from the victim's mind -- all created by the vampire's subconscious. In extreme cases, this sense of possession can drive the vampire to carry out actions on behalf of their victims.
Obviously, diablerie would be unwise for an animist to perform....
When a vampire with this derangement feeds on a mortal, a Willpower roll is needed (difficulty 6, or 9 if they drain the mortal to the point of death). If the roll succeeds, the vampire is tormented by the 'memories' of the person whose sould they have partially consumed, but is still able to function normally. If they roll fails, then the images in the vampire's mind are so strong that it is akin to having a second personality inside them, an angry and reproachful personality that seeks to cause harm to the vampire and their associates. The player must roleplay this state; otherwise, control of the character passes to the Storyteller, who runs the character as if the mind of the victim is in control. During the moments just before dawn, control automatically reverts to the vampire."