My party is as follows:
Zidane with maxed out thievery, cheap 9999 damage.
Freya with maxed out dragon crest, another cheap 9999 damage.
Steiner with Shock, yet another cheap 9999 damage.
Amarant with the Healer ability equip so his attacks heal, I just attack the party. And then he can also use No Mercy to deal out about 6,000 damage.