The Ariel Reaver was an enhancement for the Wraith blade that Raziel was intended to gain in the final stages of Legacy of Kain: Soul Reaver, presumably as he pursued Kain to his mountain retreat. Informed by Ariel that only with her soul would he be able to harm Kain, Raziel absorbed Ariel's soul into the wraith blade, creating the powerful Ariel Reaver and allowing Raziel to kill Kain and gain the Amplified Reaver. Like the Amplified Reaver, the Ariel Reaver was a permanent enhancement which replaced his other wraith blade enhancements, though it is unclear what special abilities it had, if any.
Despite being removed, the blade can be activated in game through the use of the debug menu, revealing it was a golden blade with a white core. No special abilites were present in-game.[SR1]
There is confusion to as to how Raziel would have imbued the Ariel Reaver; despite her being bound to the Pillars, Ariel's final dialogue suggests her death scene may take place at another location - probably Kain's Mountain Retreat - This is similar to the way in which Ariel's soul is moved through time and space when the Spirit Forge is activated and Spirit Reaver imbued in Legacy of Kain: Defiance.
The Ariel Reaver concept was eventually modified to become the Spirit Reaver, planned for inclusion in Soul Reaver 2 and finally seen in Defiance. Both blades are imbued by the 'death' of Ariel and are all powerful super weapons obtained near the conclusion of a game.