Thanks for giving my game a try and the feedback!
I do want to add more sounds, like background music/ambiance and swimming effects but it's hard to find something suitable in a short time. Since RPGMaker's pre-made sound assets don't have anything that fits, I'm very rush in making this game.
I think I can make the movement more smooth and add some more leniency for input if I have more time, I don't think it's RPG Maker false since RPG Maker does allow you to change most of the thing by js.
Oh ya, if you are interested to see more interesting usage of RPG Maker , check out my first game jam game:
https://catesgamedev.itch.io/rpgmaker-maker
It's my proudest creation so far since I join that game jam using all premade assets, I have more time doing the mechanical/program eventing part of the game engine.