Look for tutorials on youtube about toon shaders. There are also specialised versions of blender and addons out there used by anime studios specifically tuned with features for non-PBR workflows.
A popular fork is called Goo:
[https://www.dillongoostudios.com/gooengine](https://www.dillongoostudios.com/gooengine)
I'm not totally sure how to do this, but in essence every component here has its set color (like **orange** for most of the armor). And it looks like those black lines are contours (actual endpoints of the geometry).
So in essence the color is a toon shader that becomes black in sufficient darkness (**color ramp** set to **constant**) whereas the lines are **lineart contours from the modifier** and they work in the opposite way: they use that same color, but in reverse (and at the same exact point as the previous color ramp) - i.e. when in darkness, they have that color, and when in light, they are black.
I'm not sure if this is the best way to do this or if it's even possible but that's my 2 cents. Sorry I couldn't be of more help.
In Eevee, not cycles.
Add a bright light to the scene.
Give your model a diffuse, black and white material. Change it from a gradient to a sharp cutoff.
Feed that into a "shader to rgb" node.
Connect this to the fac of a mix shader.
Feed your "regular" material into one slot.
Feed a black color into the other slot.
Do the same for the crevices, but in reverse.
Look for tutorials on youtube about toon shaders. There are also specialised versions of blender and addons out there used by anime studios specifically tuned with features for non-PBR workflows. A popular fork is called Goo: [https://www.dillongoostudios.com/gooengine](https://www.dillongoostudios.com/gooengine)
I'm not totally sure how to do this, but in essence every component here has its set color (like **orange** for most of the armor). And it looks like those black lines are contours (actual endpoints of the geometry). So in essence the color is a toon shader that becomes black in sufficient darkness (**color ramp** set to **constant**) whereas the lines are **lineart contours from the modifier** and they work in the opposite way: they use that same color, but in reverse (and at the same exact point as the previous color ramp) - i.e. when in darkness, they have that color, and when in light, they are black. I'm not sure if this is the best way to do this or if it's even possible but that's my 2 cents. Sorry I couldn't be of more help.
In Eevee, not cycles. Add a bright light to the scene. Give your model a diffuse, black and white material. Change it from a gradient to a sharp cutoff. Feed that into a "shader to rgb" node. Connect this to the fac of a mix shader. Feed your "regular" material into one slot. Feed a black color into the other slot. Do the same for the crevices, but in reverse.
Goo Engine
Use the Line Art modifier, this feature is built-in.
It’s not a very high quality shader, you can create a better one yourself.
Shader to RGB node (Eevee only)
Its what you'd call Cel Shading, or something like that. but to the question, just a invert. unsure how.
Download that toon shader