I guess if Applebloom is the Setsuko and Applejack is Seita, then Big Mac is probably the father who was in the army/navy (?) and never came back and Granny Smith would be the mother who died after the bombingI like seeing crossovers like this, even though it's very sad, I can still imagine it working well, and it can bring MLP-fans and watchers of Grave of the Fireflies together