Well I for example noticed that there is banding happening all over the place (especially the legs).
Not sure if this is important but I personally don't like it.
I'm not sure how relevant banding is with a high-res pixel art like that though
Other than that I personally have no problem with the sketchy outline, some people may not like this kind of pixel art obviously, but it's done pretty well in this case (you could maybe add a bit of depths to the inner strokes though, but not a big deal to me).
I feel like Seiseki's ears are really doing the art justice. However, while I felt yours being oversaturated, I feel like Seiseki's red is a tad bit undersaturated. So with my edit I tried to find a nice middle ground
Also I removed the "shininess" of the stockings since these are generally very matte, and the color of yours seem to indicate exactly that