Cacoethe

When a selkie's Coat trades white for silver and black, it's time to enter adulthood. They do this by roaming the ocean alone for two years – just them, an eternity of saltwater, and mortality staring them in the face. Ten percent of them die. The other ninety percent learn some heard truths about who they are, and which parts of themselves aren't worth sacrificing to survive.

Brielle is a week into hers when she finds a merman on the continental shelf. He's weird and dying; she's bored. So ...