Thank you so much for looking into it in detail! I would never have figured it out myself...
I didn't take into consideration the player's PC language environment at all. It was a complete blind spot.
I'll do my best to address it.
Viewing post in EXOrcist GUNNER v1.0.1 (Full Release) comments
No worries, hope you'll find a workaround :) An easy fix if you have enough control on the save format is to convert everything into base64 before saving. That way you don't have to change anything to your current save format. Not 100% certain how kanjis handle base64 conversion, but I don't think it should be an issue (hopefully).
Good luck!