Age of Myth by Michael J Sullivan

Since time immemorial, humans have worshipped the gods they call Fhrey, truly a race apart: invincible in battle, masters of magic, and seemingly immortal. But when a god falls to a human blade, the balance of power between humans and those they thought were gods changes forever.

Now only a few stand between humankind and annihilation: Raithe, reluctant to embrace his destiny as the God Killer; Suri, a young seer burdened by signs of impending doom; and Persephone, who must overcome personal tragedy to lead her people. The Age of Myth is over. The time of rebellion has begun.