Longinus Copies are Divine Armaments.
They are forged by top crafters of magical equipment, these are replicas of a piece of legendary class «Magical Equipment», the «Lance of Longinus», a holy lance that vanquishes darkness. They were particularly powerful against spirits carrying the darkness attribute.
More importantly, these weapons carried a special effect. All it took was the infusion of simple «Search» magic and they could automatically seek out the direction of darkness spirits.