Been asked by a couple people about more info about them so I'm putting it all here for now.

Cheeky, silly, playful, will test your limits and later regret it. Doesn't want to be too much but often acts before thinking.
They're more of a monster than a fish, can breath out of the water. There's some magic in them, as they can make their neck longer or smaller and change size at will. Usually prefers to be bigger than other living creatures in the surroundings, but will allow herself to be smaller in very specific situations and around very close people exclusively. There's a catch about making their neck longer or shorter, as it changes the size of their tail too. Shorter tail for longer neck, longer tail for
shorter neck.
Eats mostly fish but has a soft spot for fruit. Doesn't eat people for nourishment (might do it for fun). Doesn't respect personal space at all. Talks A LOT.
The little green string on their right wrist was a gift from a friend (deer) and even thought it didn't have much meaning they took it to heart and use it as a charm for good luck, believing it's magical.

With new people she tries to look scary, to look bigger and to speak only if necessary. Acts more like a wild animal in that regard (the acting up her scaryness being a way of self defense), but leans into her more teasing side when she doesn't feel threatened. That is, unless the stranger seems to need help, in which case she'll try to do so calmly or preferably without being seen.
They're known more as a cryptid than anything else. She always tries to make a fool out of cryptid enthusiasts. Never letting herself be caught on pictures and leaving fabricated proof that "something" is there but that looks too exagerated to be believable. Only gets closer to give them a scare or steal their cameras.

Their friends aren't too happy with this, and would prefer if they remained safe and hidden instead of engaging with cryptid enthusiasts and the likes. But they'd help her in any way they can too.