From Pathfinder Lost Omens Hellfire Dispatches, which isn't enabled.

Unassailable Enforcer

FEAT 8

Prerequisites Pure Legion Enforcer Dedication

Your faith in the Pure Legion protects you from spiritual harm. You gain resistance to spirit damage equal to half your level. This resistance is doubled if the effect that caused the damage has the holy or unholy trait.

Pathfinder Lost Omens Hellfire DispatchesORC