The Haniel is an enemy from Final Fantasy III, fought in the Cave of Shadows. It divides into two when hit by a weapon other than a Dark Blade or inflicted with Paralysis. Therefore, bringing an Ancient Sword helps with dealing with these enemies for non-Dark Knights. They are moderately powerful otherwise, like all enemies in the cave.
Haniel, also known as Anael, Hanael, or Aniel, is an angel in Jewish lore and angelology, and is often included in lists as being one of the seven archangels.