
Yukâ was the sister of Riyâ, both were the daugthers of the old Easterling emperor Sagông of Shên.
According to a legend Riyâ and Yukâ, who were great Amazons and warleaders , had defeated two of Sauron's Wraiths in battle and took their rings.After their triumphal return to Shên their aging father demanded the Rings to be given to him, but the Rings eventually overcame Riyâ and Yukâ and they slew their old father.Both then became Wraiths, enslaved by the rings they had taken.
Notes[]
In Middle-Earth: Shadow of War Riyâ and Yukâ are two rogue Nazgûl who became Ringwraiths after having taken two of the nine rings of power from two Nazgul they had defeated.However this alternative universe version is quite unlikey, since the Nazgûl, after having become Ringwraiths would not have been able to be destroyed with their rings and the one ring still existing.Also at that time the Nazgul did not wear their rings , but Sauron was wearing them.If the sisters had indeed defeated two of Saurons Wraiths and taken their rings these could have only been two lesser Ringwights.
Original form in SoW: Yuka