Sorry for the double post, but since this is completely unrelated...
I just found out that the game does seem to keep track of character usage, even though it doesn't show usage percentages or anything in-game like MBAC PC and MBAA PS2 (and it does not seem to keep track of best combo/damage, but does have enough room for it).
Since it's not viewable in-game, you have to use a hex editor on System\_AAPlayData.dat. If I'm correct, the amount of times a specific character has been used by a player (rematches don't seem to count spearately) is at the address 0x18 + 0x10 * [hexadecimal character number]. I don't know all the character numbers (and don't want to try figuring out), but I think I have an idea of some (though they could be wrong):
0x00: Sion
0x01: Arcueid (possibly correct)
0x02: Ciel (possibly correct)
0x03: Akiha
0x04: Hisui and Kohaku
0x05: Hisui
0x06: Kohaku (likely correct)
0x07: Tohno Shiki (confirmed)
0x08: Miyako (confirmed)
0x0B: Sion Tatari (likely correct)
0x14: Aoko? (haven't used that many other characters too much, and 21st character does make sense)
0x1C: Ryougi Shiki (likely correct, but doesn't match up with how I figured out the first few)
There's probably an easier and/or more accurate way to figure out, but I mostly used the high score rankings, since they're in the same file (character used[?] is at 0x2B0 + 0x20 * [record number from 0]). However, it said Ryougi Shiki was character 0x21 when there isn't even that many playable characters.
Also, it has the space to record 16 bytes of character uses, which would be (18,446,744,073,709,551,616 ^ 2) - 1 uses of a character, though I don't know if it's programmed to be able to actually record that many, considering that typical calculator programs can't even show that number without scientific notation.