(your console's unique bootrom file, typically dumped via GodMode9). Steps: Place 3dsconv.exe and boot9.bin in the same folder.
: This is the most reliable "portable" method as it requires no PC software beyond moving the file to your SD card. Place your .3ds file in a folder on your SD card. Boot into GodMode9 (hold START while powering on). 3ds to cia converter portable