Valin was a specially trained warrior, chosen and prepared from birth to wield the power of the Wraithborn along with his sister Kiara. When Melanie Moore first became Wraithborn, he tried to get her to give him her amulet so he would have the power he had been expecting all his life.
However, they both learned that the Wraithborn power isn't trapped in an amulet, the power is passed from Wraithborn carrier to carrier. Therefore, it can only be passed when the original host dies.
Defeating Brijit, Valin and Melanie left together to try to figure out how to move the power without killing Melanie.