Mm, seeing how my story mostly takes place on a boat there are few characters yet to really show up. Everyone important is, well, already on the ship. Bar one of the main characters: but he shows up next chapter, so does that even count?
Well, it does now:


Esmerlin.
He is the main merfolk we meet. Enslaved by a circus, enslaves by pirates, can't catch a break but also doesn't seem to want to. He's fed, clothes, and given shelter with no need to brave the unforgiving sea and fight other mermaids to keep his area of the sea safe. He isn't strong, any other merm would eat him alive. Being a pet isn't as bad as people think it is, if you asked him. He's a smart ass and struggles a lot with expressing his emotions. If you asked him he'd claim to be more demon than human, but dude really does have a heart under all the "fae-like" thought process.
Another character who we don't see for a loooong while yet is the big bad:

I only have a rough sketch of her. Unlike Esmerlin she is what a real mermaid should be. Heartless creature who sees humans as lesser, the great sea serpent who'll sink any vessel who crosses her (Not buddy up to the crew like SOMEONE.) and slaughter any mermaid that wanders into her waters. She has her reasons, of course, but who doesn't? And truly they seem petty compared to the strife she's caused the captain of the ship's crew...