Short demo, I see. 1 minute as a girl, 1 minute as a boy, credits.
The background and foreground are merging, here we go again.
Here's an example of how to separate a character from the background using only black and white. Heavier black outlines and more ambient occlusion:
Or even better, use a gray fill. Example from "INORAVEN":
Most likely, this is digital, just stylized as a pencil, so no one is stopping you from using the gray layer. Pure mono black and white is difficult for the eyes. This is how grayscale will immediately change the picture:
