One

In this universe some people were born half-human. There are two main characters:

Kane and Kenji.

Kenji is an ex-assassin, Kane is the captain of a large ship and a very powerful crew.

Kane is a half human, along with Kenji, Kenji is half mermaid while Kane is half shark. Both being aquatic shifters, they share an attraction towards the sea.

Everyone has a soulmate, but there are rules to meeting yours, and hopefully specific circumstances lead you in the right direction.