I don't know Alphonse and Sharena are pretty strong already.
If we're going to go all crazy though:
Anna - Special - 'Anna's trick' - 5CD - If unit's HP > 1 and foe would reduce unit's HP to 0, unit survives with 1 HP. If special activates during combat and unit is adjacent to ally, after combat unit can move again with Noatun's Effects.
Basically Miracle+. Fits with the mystery shop girl behind enemy lines and also would explain whyyy she's some kind of commander or whatever.
'Oh my Axe, let me just...'