Valkyrie duology (Amanda Hocking)

As one of Odin's Valkyries, Malin's greatest responsibility is to slay immortals and return them to the underworld. But when she unearths a secret that could unravel the balance of all she knows, Malin must decide where her loyalties lie and if helping the blue-eyed boy Asher enact his revenge is worth the risk to the world and her heart.