CIA files are used for installing games and content on the Nintendo 3DS through tools like FBI (Freedom Installer) or other CIA installers. These files are essentially decrypted and prepared versions of 3DS game cartridges that can be directly installed onto a 3DS console, provided it has a custom firmware (CFW) installed.

For the uninitiated:

no official release or official CIA file Nintendo 3DS . While a 3DS port was part of the original Kickstarter goals, it was ultimately scrapped in favor of the Nintendo Switch version due to the 3DS being discontinued.

The 3DS is an incredible console for JRPGs—play Radiant Historia , Shin Megami Tensei IV , or Dragon Quest VII on it. But OMORI belongs to more powerful hardware. If you see a YouTube video claiming to have a "100% working hot CIA," they are lying to get views.