Every Sacrier has access to Angrrr, even without this passive equipped. Sacriers start the battle with Angrrr proportional to the amount of HP he/she has. If they take damage the value goes up (the specific amount is based on the amount of HP% lost). If they receive healing, the value goes down. A Sacrier's Fire spells are designed to increase Angrrr by causing damage to the Sacrier when the spells are cast. Angrrr is treated as a percentage amount, from 0% when "empty" to 100% when "full". i.e. 1 point of Angrrr is effectively 0.9% of max HP.