You might ask: Why not just download the update from the Nintendo eShop?
For a legitimate, region-matched Japanese 3DS, you would. However, the “Update CIA” exists for three specific use cases:
Crucial Warning: Do not confuse the Update CIA (a small ~500MB patch) with the Full Game CIA (a 2.1GB file containing the entire base game). This article focuses solely on the update.
In short: The update CIA is mandatory for any serious hunter.
Step 1: Prepare the SD Card
Step 2: Launch FBI
Step 3: Locate the CIA
Step 4: Install the Update
Step 5: Wait for Verification
Step 6: Exit and Verify