Harbinger by Geneva Lee

When her magic manifestation ceremony goes horribly wrong, Arden Icaros is branded with a forbidden stellar mark that names her the "harbinger" of a devastating, kingdom-ending war. Forced into hiding to escape immediate execution by the noble houses, she must rely on the crown's most feared executioner, Bishop Marius, who chooses to protect her instead of killing her. Together, they navigate intense political conspiracies, lethal assassins, and a dangerous, slow-burning attraction while uncovering secrets that threaten to topple the realm.