From Edge of Darkness Wiki
Slasher p. 127
At least one altered tenet of Morality|
You know that what you’re doing is right. That passion burns within you; the fire of certainty scours all doubt from your soul. When you kill, you are whole again. When you kill a person in a fashion that is not a violation of your altered Morality, you regain a point of Willpower. You can use this ability once per session.
You have to remain moral in order to know right from wrong. Your Morality must be equal to or higher than the level of the altered sin.