"Ghosts of the Sea Moon (Saga of the Outer Islands Book 1)"

Rafe is the God of Souls. His sister, Manume, is the Goddess of the Moon. Their battle will decide the fate of the living and the dead. Banished from his ancestral home for showing favour to mortals, Rafe sails the seas as the captain of the Celestial Jewel. Caught between two worlds, the mortals and the gods, he exists as a wayward saviour collecting the ghosts of drowned sailors before they can be devoured by malicious sea monsters. An insane Manume wreaks havoc from the Isle of Bones, sending her monster children out into the world to unleash destruction. Heedless of the consequences, she now seeks greater revenge, and her violent actions put everyone in peril. To end his sister’s madness, and protect the mortal realm, Rafe must confront his past and his estranged family. He must persuade them to help, convince them that the Goddess of the Moon is a true threat. For Manume has become more powerful than anyone could have predicted, and he's not sure he can stop her. And if Rafe can't, the entirety of existence could be destroyed.