Ahoy! Here's a quick paintover I did to try and add some more volume to the image. The main thing I noticed is that you didn't have many hard edges on your shadows. It was all soft edges, which are exactly what they sound like: they're soft transitions between light, shadow, and mid-tone. Soft edges are great for rounder surfaces, but you want to try and have a mix of hard and soft edges, especially when working with an anime style (which exclusively uses hard edges on their characters, outside of a rare few studios with big budgets). Hard edges make the different shapes in your drawing pop by creating sharp contrast. So if you were using the airbrush or doing a lot of blending, I'd recommend throwing in some harder brushes. The main places you'll find hard edges on the body will be cast shadows. Hair creates cast shadows over the face, which have very hard edges. The nose and brow ridge will also create very intense cast shadows with hard edges. Think about any part of the body that is overlapping another, where it's blocking the light from another part of the body. Those are the places where you'll get cast shadows and harder edges. Soft edges occur more around form shadows. Form shadows are where the light source is more directly hitting an object (with nothing blocking it), and the light is then forming around the object's volume. This creates a more gradual transition between light and shadow, and thus a softer edge. So things like the top of Law's arm would have a more gradual change between light and shadow. You may notice, however, that I have hard lights on his arm. This is a stylistic choice. You can do an entire piece with just hard edges (as most anime does due to how animation works). I did hard light edges on his arm and face because they create a sharp contrast and make the muscles and the planes of his face stand out a bit more. Also, when adding shadows to the face, you get a lot of bang for your buck by adding deep shadows to the upper lip, the bottom of the nose, and under the brow ridge. Unless the light source is coming from below, those places will usually be in deep shadow, and rendering that will immediately add a lot of volume to the character's face. I hope this was helpful!
