Not sure if anyone discovered this, and I found this while messing around with Akiha.
But when I do Akiha's Arc Drive and spam A, B, or C, while she is doing it, There will be more hits, more damage and it makes this scratchy sound. ( Sounds like Wara's 623C or 236C )
If you don't understand. Download the replay and you'll see what I mean. >.<
Also the only other characters that do the same thing is V Akiha.