Children Of The Nameless by Brandon Sanderson

A cursed young woman whose nightly song once protected her remote village from the horrors of a haunted land seeks vengeance after a massacre shatters everything she knows. Forced into an uneasy alliance with a sardonic, contract-bound mage who’d rather nap than play hero, she unravels a web of demonic bargains, vengeful spirits, and a forgotten power that steals names and identities. Together, they uncover the truth behind the killings and race to reclaim what was taken before the encroaching darkness consumes the last survivors.