MH4G to MH4U savedata transfer notes

Yesterday night I finally managed to transfer my Monster Hunter 4G savedata to Monster Hunter 4 Ultimate. Hooray! Shout-out to the smart reverse-engineer who solved the final encryption issue and shared his work with me. I promised some people to do a small post about this since they were interested when I first mentioned this, so now that it works, here we go.

Disclaimer: You require quite a few very specific pieces of hardware and software to pull this off so don’t get your hopes up if you’re a 4G player - this post is adressed to people who are interested in what’s done “behind the scenes”. Since the 3DS homebrew scene is currently on fire, things may get less messy and this routine might be outdated soon (hopefully! lol).

Prerequisites:

    Retail/Digital copy of MH4G
    Digital copy of MH4U
    EU/US 3DS on Firmware <9.2
    JP 3DS on Firmware <9.2 (if your save is digital and/or you want your extdata, s. below)
    Gateway 3DS
    3DS cartridge reader + accompanying decryption tool (if your save is on a cartridge duh)
    Nintendo SaveDataFiler (consult Google, leaked SDK tool)
    MH4G de/encryption tool (not allowed to share this, maybe the aforementioned RE will publish it sometime, idk)
    Hex Editor of choice

1. Obtaining the MH4G data

I will assume you are familiar with how to handle Gateway 3DS EmuNAND etc there are enough guides out there if you’re not.

If you play on a digital copy of MH4G, this is easy. Boot into EmuNAND of your JP 3DS, load up the SaveDataFiler utility (ROM/CIA… either one works fine). Head to the User tab and find 011D7 (MH4G ID). Press Y to export the save to the SD card. Head to the Ext tab, again find 011D7 and press Y to export it. Extdata includes: unregistered guild quests, guild cards, saved armor sets, download quests, SpotPass stuff. So nothing too important but nice to have it carried over.

If you play on a retail copy of MH4G, things are a bit different. If the 3DS you play on is <9.2, you can follow the above guide to retrieve your extdata. Apart from that, pop-in your cartridge to the USB reader and let the tool that comes with it decrypt the savedata so you get plain system, user1, user2, user3 files (depending on how many characters you created).

If you used SaveDataFiler to obtain any data, copy the corresponding folders and files from your SD card (all stuff extracted by SDF is stored in /filer/ directory in the root of your SD card).

2. Prepping the MH4G data for 4U

Unfortunately, we cannot simply inject our MH4G savedata to MH4U as the localisation team decided to change things up a bit. Namely it’s just one change but it breaks your guildcard if we don’t fix it: the character limit for your guildcard description text which is now 36 chars longer and therefore takes up 72 bytes more space (due to the game using UTF16-LE encoding).

By the way, the localized version does not support Japanese characters, so make sure to fix your name or whatever else important you use Japanese chars in in this step.

If you haven’t acquired plain text savedata yet, decrypt the files (pointless to go into detail since I can’t give out the tool and it’s not released yet). MH4G/U uses an additional layer of encryption for savedata and extdata which no other 3DS game I know of (except for MH4) does.

Open user1/user2/user3 in your Hex Editor of choice and jump to offset 0x12738. Insert 72 bytes of nulldata. Jump to 0x139F8 and you should see some dummy data. Remove 72 bytes of the the nullspace before the dummy data to make up for the changes. Save your file. There we go! Your user savedata is now fixed and almost ready for 4U.

The same problem applies to the card1~card3 files from your extdata. These are the only files from extdata you need to decrypt. Since you may have lots of guild cards stored there, it might be worth wrapping up a little script (pretty easy, start at 0x148, insert 0x48 bytes, move by 0x1200, insert etc.). I did it manually since I only had a few cards anyway and had to verify the guildcard size is always identical. Don’t forget to cut out the added 0x48 bytes at the end of each guildcard block.

To wrap up this step, encrypt user1~3 and card1~3.

3. Injecting our prepped data to 4U

Not too troublesome, huh? Well, time to finish this. Create a dummy char in MH4U, save and extract the userdata and extdata just as in step 1 but this time look for ID 01261 (EU, no idea about US).

Mount your SD card, navigate to the newly extracted data and replace the present files with the encrypted user1~3 and card1~3 from the previous step.

Run SaveDataFiler for the last time and go to the SD tab, find the extracted 01261 user and extdata there and import it. Done! Your MH4G savedata, guild cards, armor sets, etc. have all been successfully carried over to MH4U.