The game you are referring to is likely (released in 2011), developed by Griptonite Games and published by Sega for the Nintendo 3DS. Game Details Title: Shinobi (often referred to as Shinobi 3D ) Platform: Nintendo 3DS Genre: Action / Side-scroller Publisher: SEGA File Formats Explained
While the original 3DS hardware is region-locked, "Region Free" CIA files have been patched to work on any 3DS console regardless of its original region (USA, EUR, JPN), provided the console is running custom firmware (CFW). Where to Find it Shinobi ROM & 3DS (USA) CIA (Region Free)
I can help you with the specific installation steps for either. The game you are referring to is likely
You can often find these files on archival sites like the Internet Archive or community-driven ROM repositories. You can often find these files on archival
This format is used to install games directly onto a modded 3DS system's Home Menu. They function like an "installer" package.
3DS ROMs & CIA Files: A Complete Guide For Citra Users - Ftp
This is a standard ROM format typically used with flashcards (like Gateway) or PC-based emulators like Citra.