Kyoko

The AU is set years ago in the era of pirates and there are sirens (I know I said mermaids but they're actually sirens). Cole, Jay, Zane and Pixal (Zane and Pixal are humans) are pirates; Kai and Nya are sirens and Lloyd is a hybrid.

First off, sirens. Sirens are predators who decieve and hunt humans using their melodic voice and appereance. Sometimes they eat the humans they've hunt down but most of the times they eat other fish. To decieve humans they can change the upper part of their bodies to look human; all sirens are intersex (each one with more masculine or feminine traits) so they can change into both male and female humans (Kai is usually a man and Nya a woman but they sometimes change). Sirens can form groups or hunt alone. Kai and Nya lost their parents when they were little and have been on their own since then, barely having any contact with other sirens. Most sirens have blue to green characteristics but sometimes there are ones with other colors like Kai; that's usually a disadvantage since it atracts other predators.

Kai doesn't like humans at all and usually fights other sea creatures (like sharks). He doesn't like deep waters either.

On the other hand, Nya is interested in humans, mostly their inventions and is really curious. Unlike Kai, she does like really deep waters. They're both very protective to each other and Lloyd.

Then, Zane and Pixal had an arranged wedding they didn't like (Gay and lesbian solidarity) so they decided to run away and join the pirates, the ones of the Destiny's bounty.

Cole is a member of the pirates and became one to find a treasure and get money for his village. He often feels bad because he couldn't afford his mother's medicine and he blames himself for her death.

Jay has been a pirate for the longest time. At first he just wanted the adventure but then he kind of regreted his decision (until he bonds with everyone). He's really skilled.

The captain of the Bounty is... an asshole so... mutiny(?) , eventually Cole will be the captain (because he is a good leader) and Jay the second in command.

As for Lloyd, he is a hybrid: Misako is human and Garmadon a siren. Wu and Garmadon are considered mythical creatures so Lloyd is basically unique. He lives in a small house next to the sea after Misako passed away. When he was a kid he had an encounter with Kai and Nya and, after a while, they became friends. Now Kai and Nya have adopted him as their little brother and go visit often. Lloyd treats their wounds as well as other sea creatures, he's a healer (vet?). Eventually he'll go with the Bounty's crew.

As for ships obviously plasma and samurai but also glacier.