The Soul Keepers by Devon Taylor

Rhett always thought that death was the end of everything. But after he dies, he discovers it’s only the beginning.

He awakens in the afterlife and is immediately recruited to join the crew of the Harbinger, a colossal seafaring vessel tasked with ferrying the souls of the dead. To where exactly, no one knows. But they must get them there, and they have to protect them from vicious soul-eating monsters that will stop at nothing to take the ship and all of its occupants.

Rhett and his new friends have a hard enough time fighting back the monsters that grow bolder and more ferocious every day. But then a new threat emerges, a demon who wants something that Rhett has. And if she gets it, it could mean the end of everything... for both the living and the dead.