Beg the Night by Emily Blackwood

Athena is an earthly. She wields no power, and though war rages across the lands, she lives a relatively normal life in isolation until she’s kidnapped by the Ministry and questioned for the magic they’re certain she possesses.
As she struggles to grasp her new reality, she’s forced into a dungeon with dozens of mystics. Only to discover she’s the only female.
True unleashing of power can only be obtained by the claiming—a mating ritual under the powerful blood moon. But Athena is in luck. Those mating must be willing, and she is certainly not willing to come within a foot of any of her options.
Until she meets Sinner.
Sinner is a tier three—the only three in the entire dungeon, making him the most dangerous and powerful of the men. He has very little interest in getting along with others and prefers to live his life alone.
So it comes as a shock when he volunteers to complete the claiming with Athena. She’s his ticket out of that dungeon, and she knows it.
The two struggle for the upper hand as Sinner tries to convince Athena to mate with him willingly.
But Athena resists. She has a secret, and it’s one the Ministry would do anything to get their hands on.

Can she keep her secret hidden long enough to survive? Or is Sinner the one person who will expose her for what she truly is—a monster?