My 3DS's circle stick thing broke, so I decided to trade my 3DS with someone else. Luckily, everything transfers via SD card... except DLC content. I had the all fighter's bundle, Cloud, Corrin, Bayonetta, and Dreamland 64 (basically everything I really need, except Inkling. I want that Inkling some day). I don't believe I should have to pay for the DLC again just because they used cheap plastic for a crucial component of the system. So, is there any way to get it without repaying for all of it?
Did you buy a new 3DS and do the system transfer? If you didn't do it and just save the SD card that was on your 3DS, you are quite in a big trouble.
My old 3DS' circle pad broke early 2015, so I bought my New 3DS XL and perform system transfer, which was a bit terrifying when the first time I tried it failed to transfer my NNID due to my old 3DS failed to connect to Wifi at that time. Fortunately the old 3DS' data didn't get wipe out (But the new one did, but there wasn't anything much there since I had just bought it.) even my system transfer failed. However I still get my old 3DS' circle pad fixed and sell it with a fair price. The old 3DS was completely empty, I don't really need to worry about my NNID or FCs since it's already on my New 3DS.
Every 3DS can only have one NNID and FCs, NNID can be created both on your Wii U or 3DS/New 3DS. If you created your NNID on your Wii U, it can be brought to your 3DS, and vice versa. You can share Eshop balance if your Wii U and 3DS has the same NNID. But the criteria is taht both Wii U and 3DS has to be on the same region. I don't really know if I can put my NNID to my brother's Japanese Wii U, but I'm not gonna try that.
And doing the SD card transfer was also kind of disturbing, I have experience when my SD card data get corrupted due to many reasons like your SD card's quality, your PC/laptop, etc.
If you did do system transfer successfully and use the same data/SD card. Your DLC should be there. And even if your SD card's data got wipe out, you should be able to redownload everything you purchased on eshop for free. But your save data are lost forever though...
