Sasuke's Kunai - Ninja tools are consumed at 1/2 rate. Meaning it takes 2 shuriken throws to equal 1 shuriken. Only works with Ninja items like Shuriken and scrolls.
And is broken so it doesn't consume any if you only use only one in a battle.

Man, it's been so long since I have gotten to FF6 that I don't feel current enough to give this a shot.