War of the Myth, book 2: Think of Me DemonMiranda Grant2018

For her to live, her lifemate has to die

Matakyli is a demon warrior princess and one of the guardians to the backdoor of Niflhel. Her death could lead to the dead escaping, bringing about the annihilation of the Seven Planes. So when a prophecy claims she will be killed by Sebastian the Ancient Destroyer unless she has the powers of her lifemate, her brothers kidnap the man and chain him in their dungeons. They will take her lifemate's power, whatever the cost.

They will pay for what they did to him

After being sold into slavery as a child, Galvanor swore he would never be helpless again. Now an Elv've'Nor, a guardian to the Seven Planes, he's kept that promise for over sixty years. But then he wakes up imprisoned in a cell deep in the Underground, chained and collared, with his telepathy restrained.

His capturers believe him to be helpless. They couldn't be more wrong.

Able to dreamwalk, he visits Matakyli at night, and now the hunter has become the prey.