Whenever a Being murders another, a Soul is released. Many people use this to become more powerful, as they defile their nature and devour the Soul of their victim. Though not inducing a sense of taste, this phenomena will increase the thirst for more Souls. The addiction and the mutations following the continuous consumption of Souls is known as Soulmaw.
Those that dwell in the act of soul consumption become beasts in time. Those are known as Souleaters and are feral beasts hunting down the living for their Souls.
The addiction becomes obvious when the person becomes more agitated and erratic in fighting. Whenever a Being with a Soul is slain, the addicted persona strives to receive the earned Soul first.
Throughout the increase of need for Souls, the person becomes more aggressive and seeks opportunities to fight people. This aggression increases to the point that the person is irrational and antisocial in behavior.
At a later point, a Soulmaw fully turns into a Souleater by losing all rationality, becoming a feral beast that hunts for its now one and only nourishment, Souls.
Eating a total of 10 Souls of Beings more powerful than a Human (basically anything but human) is the first step to become addicted. The character has to roll a Constitution check against 2 for the 10th Soul and each third Soul in succession. Should the character succeed, the person does not get addicted yet.
Once addicted, a character has to roll against composure (WIS+CHA) against 2 every time the character encounters a free Soul. When the composure does not succeed, the character will do whatever it takes to eat the Soul. Again, a Constitution check is needed for each third Soul consumed. The difficulty for both the composure as well as the CON roll increase by one for each lost CON roll.
If a character comes to the point that the composure and CON roll are on the difficulty of 8, the character permanently becomes a Souleater, losing all sense of rationality. At this point, the character becomes unplayable.