The move comes from a ring, called the Darkwood Grain Ring.
To get it, you have to be a member of the Forest Hunter covenant, and have access to the lower section of Blighttown.

Head down the waterwheel and kill any enemies along the way. At the bottom of the waterwheel near the ramp, you'll see Shiva of the East from the Forest Hunters (if you're in the covenant). He sells weapons. Going behind him, though, you will see a shadowy character underneath the ramp leading to the waterwheel. This shadowy ninja character has the ring. I don't recommend attacking him, but lead one of the fire-breathing monsters to him and position yourself so that the ninja is preventing the monster from getting to you. Hold up you shield, let the monster breath fire on him.

He'll die and drop the ring. This makes Shiva want to kill you, though, so that kicks you out of the covenant and you have to absolve your sins. At least you'll have the ring! It's pretty nifty.