Soul Eater

The Soul Eater is Riku's weapon in Kingdom Hearts and Kingdom Hearts: Chain of Memories. It was made of the darkness inside his heart, "forged" into its sword-like shape by Maleficent's magic. The Soul Eater is also used by Vexen's Riku Replica. World of Chaos even had a double bladed pole arm version of it. It looks a bit like a dragon wing.