Song of the Abyss by Emma Hamm

Like a songbird in a cage, Anya has spent her entire life as the General’s perfect daughter. He snaps his fingers, she jumps. He tells her to smile, she beams like she is made of the sun itself. But underneath all those games and glitter, she’s working to destroy her father and save the city she loves.
When an undine sneaks his way into her city, intent on kidnapping her, she lets him take her.
Daios is plagued by the decisions of his past. Souls haunt him, memories follow his every move, and all he knows is that perhaps stealing this woman will absolve him of his sins. If he can bring her back to his people, then they can destroy the city where his hatred was born. He’s certain this will be easy. But then he sees the General’s daughter, and he knows nothing will ever be the same again.
Broken and damaged, he’s certain no woman will ever love him. He shouldn’t even try to encourage the mating instincts that ride him hard the moment he sees her.
But when he realizes that she’s the same as he is, different from her people and on the outskirts of what others deem “normal”, he knows he’s a goner. Even if it means he has to risk everything to keep her.