Hey, this game is super cool!
The grappling and shooting mechanic is somewhat unique to what I've seen, and it has some very interesting implementation as a platformer. It feels really satisfying to pull of some sweet moves and super close saves, as well as the feeling of swinging around the stages like Spiderman!
If this really is a story-driven game, what would make this a full game is, well... the story! Really solidify what you want the lore to be, the message of the game if there is one, the characters, and expanding on the mechanics. In my opinion: A good story game is one that creatively uses game mechanics to tell that story, and one with characters that play pivotal roles in getting a message across to the player.
I like to ask myself questions when thinking about this. For instance, who is that green cube? Why can it both grapple and shoot? Is the tether a part of its body, or has it acquired it somehow? Why does it look so scared when using it? Could this imply that grappling and shooting is new to this creature, or that it doesn't really enjoy using it? What about the tutorial? Who is giving us all that advice, and why? Are they helping us? Or is it not meant to be meta and is just a tutorial lol
What is this green, isolated world? Why is it so empty? Who is the typist, and what do they want? Where is the typist, and why would they leave a note instead of just speaking directly? What about that one guy? Why is the green cube late, and why are they often late? Who do they work for?
I could go on, but you don't have to answer these; Just stuff to think about when developing a deep story for this game. I'm interested in seeing where you bring it!
I could use your input for my game as well: https://wasabiiii.itch.io/grass-elemental-demo-demo
Great work! Oh and I meant to ask, is Kevin III the father of Kevin II? That's cool, it's like a family-developed game :)