Hello! Thank you for asking~
For characters, you can use them commercially since I drew them myself, but it must be linked back and credited to my itch.io profile so other people can find and use them too. For backgrounds, I suggest that they only be used in non-commercial games since I have used royalty-free stock images from non-commercial sites. I've only edited the stock images to make them, I didn't draw it all myself.
I'm not surprised that there are more western materials for games overall. Not a lot of people make oriental/eastern games. Demand for them in general is lower, so fewer people make them.
If you are looking to sell your games for commercial use, you can try hiring a dedicated artist. Ertal (https://ertal-games.itch.io/) has experience in creating and selling games and might be able to help you or give you advice.