It's explained in the translation spreadsheet. Basically unlock and equip magic cancel _______ -RA/-GA. _______ being whatever move magic cancel is branching from (for example Sice' forward/backward directional attack) then you perform that move and as it finishes, press or hold the magic attack button and it'll fire out. It's really only makes a difference when you unlock -RA/-GA MC
Official ALEXANDER of the Final Fantasy Type-0 Borard _\(=/)/_???