The Aspirant of Blood by Riley Knight

The gods have abandoned us. Only when the harbinger of shadow is slain will their light return to the land.

Lady Mare Rohan is the last living heir to the lost city of Tirnanog—a title that means nothing with her people dead.
Trapped without purpose in a land that is not her home, Mare wants only to learn the truth of what stole her home away. But fate has other plans for her.
Paragons are vaunted heroes—only the Emperor himself holds more power. They carry enchanted weapons that choose their next wielder upon the previous Paragon’s death.
One just chose Mare. But women are not allowed to be Paragons.
To shield her from the enraged nobles who want her dead, the prince orders Mare to train under the most powerful remaining Paragon, but she is in more danger with him, than alone. Shadows stirred within her when she first wielded the Paragon’s blade—the forbidden magic spoken of in prophecy.

Paragon Tiernan is the only force protecting her from her enemies, but should he learn her dark secret?
He would not hesitate to take her life.