>>1012331Normal is a vector that describes light response of a geometry. By default it's perpendicular,
in advanced NPR styles and especially in anime normals are most often manually edited and deviate highly from that.
You can get non-perpendicular normals also automatically by using "shade smooth" instead of "shade flat" or with modifiers like "smooth by angle".
https://www.youtube.com/watch?v=oKfFi1MpO9c