I was just wondering if it has ever been confirmed what they do to souls? A shinigami uses can purify Hollows and send normal sould to the soul society by touching them on the forehead with the hilt.
What do the Arrancar's Zanpakuto do? Would touching the forehead of a soul with the hilt turn the soul into a hollow. Would slaying a soul with the blade feed that soul into the Arrancar?