Quick question. When you beat the game are you allowed to go back and up your ranking on individual episodes. I’ve been trying to go through and get at least an A rank on hard, but I accidently got a B rank on one and saved it. Now it doesn’t seem there’s any way to go back and redo that individual episode without starting over. Thanks in advance.
You can only improve your performance on a specific stage by replaying the game alltogether.And you can only save one “save-game” so you better be good at it 
Like Gehn said, there’s no way to go back, but if you can get a couple of S ranks your overall score should average out as an A.
I’m afraid you’ll have to start the game over to get an A for that Episode, as Gehn said. The only way to jump to individual Episodes is from Pandora’s Box, and your scores don’t save while using that feature.
Alternatively you could finish your current game on hard and then go for all “S” ranks next time around, instead.