Story has a great Plot
I like your writing style (it a sassy hint to an older English style without definitely hinting to writing styles such as medieval times English) and the plot of the story! It's something minty cool, but it needs work on a details around the events that you've put in place some more descriptions to make the story shine like I know it can!
Read the story now
You have definitely given some air of mystery to the story and at first glance over I was hooked to the idea. It's fairly well written for a first draft and from what gathered a quickly written one at that.
Can't wait for the second draft, but will, I want to completely finish reading the story once you're done with editing and adding some more details, or lighting for the story to shine through.
(Read till chapter 4) and glanced through the later chapters. Like said well written for a quick written first draft but needs more etchings and shading like a picture that the frame work is done for and now needs coloring and dimension.
A tip I can give is to build around the concept of the 'monster' the 'undine' the 'nymphs' and what 'humans' are according to the story. I was peaked when read about nymphs, but the lack of prior shades to the story made it unclear to me what nymphs are to this world of yours. but what I can make out of, it could be something/someone great! Further world-building will help you with a second draft.