The Storm Shield is a purple shield with a Lightning bolt on it. It has 4 dots on each side of the shield. The shield is great for fighting the Floor 4 boss, Ra'thae the Ice King.
It has a defense of 152 and increase of speed in 2. The stats are the same as Wind Guard.
Even though it can only be equipped at 18, it's partner the Storm Blade can be wielded at level 16.