How did I manage to lose it all, you ask?
I was stupid enough to use it to save game data from the delightfully wonderful game - naturally I can't find any information about it online and I don't know the name of the game since I didn't bother to ask Brandon and I can't read Japanese. I think what happened was that the game save data from the japanese game made it unreadable to the american games. Either that or when I started it up it asked if I wanted to format the memory card for use on the japanese game and since I don't read japanese, I just went with yes.
Time to start afresh. Unlocking things in games all over again - particularly the Mario Party games. This could be a positive thing, somehow.