Soul Eater

The Soul Eater (ソウルイーター) is a form of Riku's weapon that appears in Kingdom Hearts, Kingdom Hearts: Chain of Memories, Kingdom Hearts II, and Kingdom Hearts 358/2 Days. It is a sword that grows more powerful when used with darkness.

The Soul Eater is first seen at Traverse Town, when Riku uses it upon a Soldier that had attacked Sora. He continues to use this weapon during his appearances until he is possessed by Ansem, who uses the Keyblade of People's Hearts instead. In the final battle against Ansem and the World of Chaos, Ansem uses a giant double-bladed pole-arm version of the Soul Eater.

The Soul Eater reappears as Riku's only weapon in Kingdom Hearts: Chain of Memories, though unlike Sora, Riku can choose to strengthen his weapon as he levels up. Riku also uses this weapon in Kingdom Hearts 358/2 Days, notably in his duel against Xion, he never actually uses it while battling Roxas; in his first encounter he simply runs away from Roxas without using any weapon at all, and in his second encounter, he uses the Oblivion Keyblade he had taken from Roxas, before using Ansem's darkness to defeat him.

In Kingdom Hearts II, Riku continues to use the Soul Eater throughout his appearances, and this eventually causes Sora to realize that Riku is the mysterious hooded stranger the group had been encountering. However, by the time Riku arrives at The World That Never Was, the Soul Eater has been transformed into the Way to the Dawn. Even after this, Riku continues to refer to his weapon as the Soul Eater.

A copy of the Soul Eater is also used by the Riku Replica and Zexion's clones, when he fights Riku.

Design
The Soul Eater is a scimitar-esque sword, with a red, purple and blue blade shaped like a demonic wing. Its handle bears a blue eye. It has a striking resemblance to the Way to the Dawn, as well as Vanitas's Keyblade.

Etymology
The weapon's name is derived from an ability attributed to the Dark Knight class in the Final Fantasy series, in which Soul Eater drains the HP of the user to initiate an extra-powerful attack. The attack and the Dark Knight class are associated with darkness, and the Soul Eater ability is sometimes called Darkside or Dark Wave, making it a fitting name for Riku's weapon.