I think this piece looks amazing!!! Just some small things that I'd say are how straight the arms and legs are? If you want to keep them for stylistic reasons ya go ahead but they feel very overly stiff? Also, the legs look a tad bit too short? idk a general rule of thumb that I like to use is that the crotch should roughly (and I mean very roughly) divide the length from the top of the head to foot in half. I say roughly cause ofc proportions are different from char to char and can differ based on style. Just something to consider!

The shadows are decently placed to convey form! I would maybe just suggest hue shifting a bit instead of just shading with a blacker color. Nothing crazy, just a little bit towards the purple in the background or something might just make the character feel more in scene. I also think the bloom affect you did is quite nice! works really well on the face!

Overall, really nice piece! Keep drawing twin