The Anointed’s Paladin by Katy Black

A monstrous paladin. A bloodsucking rulebreaker. An innocent sprite.
All searching for a place to belong.
Talon, a holy Paladin with a demonic heritage, is surviving on borrowed time. Under threat of death, he accepts a thankless quest from a God he hates.

He sets out on his mission, but his heart isn’t in it, instead longing for the new life that just slipped out of his reach. That is, until his attention is drawn by a fateful encounter with an unlikely pair:
Nidori—an innocent sprite, endangered by her own pure heart.
Kaine—the alluring and deadly hellspawn who has stolen Nidori’s freedom.
Even though he is disgraced and reviled by the world, Talon cannot abandon Nidori. And in seeking to free her from Kaine, he finally finds a purpose he believes in.
Kaine, desperate to escape his own demons, meets the challenge with a game of his own—to dominate Talon’s body and soul.

As Talon struggles against becoming Kaine’s next prize, his strict boundaries between right and wrong begin to shift. And despite the promise of death, he can’t help but admit that’s faced with the truth that worshiping at this hellspawn’s feet feels like where he was always meant to be…