Prophecy novels (Ellen Oh)

"A demon slayer, the only female warrior in the King's army, must battle demon soldiers, an evil shaman, and the Demon Lord to find the lost ruby of the Dragon King's prophecy and save her kingdom"--

"Girl warrior, demon slayer, and tiger spirit of the yellow eyes: Kira is ready for her final quest to save her cousin--the young boy destined to rule the Iron Realm as crown prince--and to uncover the third lost treasure while facing innumerable enemies in order to fulfill the famed prophecy"--