Mortal Guardian by Tia Didmon

A Descendant. A Pact. A Guardian.

When a traitor reveals the reapers are turning humans at an alarming rate, and Riley’s blood is the key, a family secret is revealed that threatens her life and sanctuary within the clan.
The reapers join forces with the demons in exchange for immortality, but their pact includes experimenting on humans and shadow shifters alike. After Riley’s attempt to save an innocent results in Colton being infected with demon blood, he begins a transition into something she doesn’t recognize.
When the demon’s plan is revealed and Riley’s trust is betrayed. Will Riley kill the man she loves in order to save humanity or accept her fate and become the demon king’s puppet?