I agree that being a specific type of fan-art, the curve by which anyone judges this is a bit lower in a category, but I think it fair to judge the structural qualities independently of that idea.
So, to begin with: there is a sense of impressionism in the structure of this piece, that is: the majority of the piece's shapes are way less concrete and more "suggestions" of the shapes that exist.
The intention behind this conveys a sense of distance between the primary character and the world she exists within, to a point where our eyes are naturally drawn to *her* eyes.
The main characters' eyes are where we are drawn towards because they are concrete and detailed with lighting reflections that the rest of the piece's blurriness simply does not have. This is a powerful point in the picture that I like quite a lot.
Her expression is one of excitement and preparation. The toothiness of her grin means she's happy to be engaged in this fight, despite the exertion evident in her sweat.
Notably, the other characters have a similar layer of visual clarity to them, despite their impressionistic level of detail: they are very defined and have a lot of shape to them even though a lot of the piece lacks those details.
I think personally that this takes a little away from the blurriness of the rest of the picture, because what I gather the point of the piece happens to be oriented around how the primary character - sitting in the shadows preparing for her next fight - is experiencing the paint battle.
Though an argument could be made for her focus being on those characters, so they might have more detail to them from her perspective, so it still works as an idea.
They seem to have fairly appropriate lighting, I think that for the detail on the green Inkling boy, the lighting feels a bit hurried, but I'm not that well-trained on seeing the impact of lighting as much as I am color.
The colors here are striking and imposing, and while I think that the green in particular shifts a bit too harshly when it goes into the shadow, the majority of the piece has a lovely shiny edge to its impressionism: which is impressive because a lot of the piece is in shadow.
A lot of the paint splotches are drawn, to me, too intentionally to be as random as they might actually be in the fight, the sense that they're fluid impacts is a bit absent, but to be fair, this does contribute somewhat to the impressionism, so it's not all bad as an idea.
The character poses are fantastic in that they move, from left to right, in decreasing action: One character is dynamically moving, the middle character is reacting with activity (but significantly less than the first character), and the principle character is unmoving but *preparing*.
Add in the fact that the characters do this in a sort of "cone" shape, growing bigger as we go right, and this is another thing that ultimately draws us to the gleam in the main character's eyes.
A very good effort at conveying a character's thrill in an active and physical competition that relies mostly on the singular detail of shine in the main pink Inkling girl's eyes.
This pays off as we move to her eyes and then back out: our own eyes end up darting around the picture, much like the Inkling Girl would be in order to assess how to approach the combat situation with which she is having so much fun. C:
Good work, ErMao. :0)