Trying out a Blunderbuss

Overall, I think the piece is pretty decent and stands pretty solid on its own. I do however have some minor criticism.

For one, I think this piece might have worked better as a non-shaded, multi-nib work. Your use of ballpoint shading is well executed but it doesn't fit exceptionally well with a manga inspired style presented. Often times, the style lacks shadow or fine detail so shading can just come off as a secondary garnish to an art piece. Not a criticism of your style, I'm only suggesting that a change of medium might aid your presentation.

Secondly, I'm gaining a hunch that you didn't sketch out this drawing with pencil first. Again, the drawing is good and shows a reasonable understanding of shading and perspective, but there's little bits here and there that indicate that you take an "add on continually from an original drawing" approach instead of a "manifesting into art a perfect sketch" approach. There's no shame in it as many artists have done stellar works without sketching from starting out. But it does lead to some bad habits, most notably the justification of tangential ideas from the original idea to justify a good art piece which pretty much only serves to clunk up areas with detail. I would highly suggest getting into the habit of sketching as it can greatly improve the piece you make. Even just eyeballing an origin point and drawing from there can do wonders. And if you have concerns about erasing original sketching lines, I would still suggest making a sketched piece first then copying construction on a separate paper.

Either way, apart from my own feelings about the OCs (which I'll keep to myself with this being a commission), this piece has good perspective and vision and is very enjoyable to look at. Keep on with the good art!