Demon Sword "Desiderium"

This demon sword was sealed in an ancient ruin. The sword in itself is mediocre, but it is filled with a magic power which allows the wielder to cut only what really has to be cut. An old story even narrates of an adventurer who slew many monsters killing only the evil spirits possessing them, but nobody knows if it is true. However, judging by the mysterious glow of the blade, everyone would believe that the story is true.