
How Charles Domain Expansion couldhave worked
Taking into account design of Higuruma and Hakari, since he is designed in similar way, his domain wouldnt be extension of his cursed tool, rather pure visualization of his personality
Being more literal with "designed in similar way Hakari and Higuruma are" His domain probably focuses on giving him a reward, if he earns it inside domain
He would probably create a place with tools to draw, where sure hit disables combat for both sides and there is shikigami ordering both combanants to visualise something that would be written on a wall between both sorcerers. Once specific amount of time passes, shikigami judges both works and gives a reward to person that makes better drawing.
This would well represent Charles state: he sees his enemy as inferior in understanding art, but despite himself (on paper) knowing it, it dosent change that he got rejected, state of despair
Similarly how technically Higurma can lose a case but have advantage of being a lawyer and Hakari can miss a jackpot but try again, Charles have advantage of being a (aspiring but still) mangaka, what should let him to better express himself on paper than most sorcerers that probably dont draw
However he would probably lose to someone like Sukuna, who back in Heian era was a nerd that def knows how to paint/draw
Reward for winning would be closing domain and giving Charles (or enemy, if he ever was about to lose) cursed tool based off drawing he did instead of the one he usuallly have