Somehow

Same!!! Every….single….. one

SAME

I think it may be the faces. Their expressions or rather, lack of. Not a single character in this manhwa has a natural expression on their face. Besides the mouth shape or possibly eye size changing, nothing else changes when characters express shock, anger, etc. I can't really describe it well, but there are some stories where the artist was able to draw miniscule changes in expressions.

I KNOW WHAT YOUR TALKING ABOUT literally their faces won’t make any expressions only their mouths like when that black hair guy smirk at the crown prince his eyes stayed the same