Distributing or downloading Nintendo's proprietary BIOS, firmware, or decryption keys is generally considered under copyright law and the Digital Millennium Copyright Act (DMCA). Nintendo has historically taken aggressive legal action against sites hosting these files.
: A database file required for games released after 2015 that use specific encryption "seeds". Nintendo 3ds Bios File Download
To get these files safely, you must have a 3DS console with installed (typically via 3DS.guide). Distributing or downloading Nintendo's proprietary BIOS
If your emulator asks for system files, it is likely looking for one of the following: Nintendo 3ds Bios File Download