Your game should follow a certain style.
You can’t just mix realistic AI art with very simple pixel drawings, as they clash badly.
I was really surprised when I saw the simple pixelated characters as the loading screen was giving me a different vibe.
Check the below website, it showcases cool designs from other pixel games that you can try to imitate. By design I mean everything, from the fonts, background art, characters etc.
Games | Interface In Game ← Click here
As of now, your characters aren’t that appealing. You can improve this only by practicing your drawing skills. You can still keep them really simple, but if you do you should give them something to stand up. Maybe make their animations smoother, add an outline, give them some shadows or just add a lot of particle effects to their attacks and movement.
Also see this example, there is a trailer in this website.
Save Game Sunday Kickday: Adventures of Pip - Save Game
The character starts as a cube, but even as a cube because the gameplay is smooth you don’t really mind. You can always fight bad design choices with cool and fun gameplay. This is the reason we play games anyway, to have fun.
If you can’t get Aseprite, you can create your game art in Pixilart.
The website is free, you can download your work as pngs, gifs etc and you can also get inspiration from other members. Sometimes I prefer it over Aseprite
Pixilart - Free Online Art Community and Pixel Art Tool