The .xdelta patch file (found on reputable Fire Emblem modding forums or GitHub). Delta Patcher or xdelta UI.
If you want to look deeper into the technical differences or download community translation tools, I can provide details on or how to set up Gecko cheat codes for Maniac mode . Which area Share public link
: A difficulty setting much harder than "Hard" mode, which was replaced by "Easy" mode in international versions.