Savants of Humanity by Joshua Buller

Six years have passed since the Scholar, Hawke Morau, saved Micasa from a life of slavery. After restoring Hawke's soul, the two have journeyed across the land of Astra, the last bastion of humanity, and worked together to help their people.

But soon, a single letter sets off a chain of events that forever alters the fate of their world. With the chance to finally confront the person behind their people's struggles, Micasa and Hawke race against time to build an alliance capable of facing the demonic horde head-on.

Yet even humanity itself may stand between the two, and their goal.