Dealt 99,999 damage with a single attack.
You can easily do this against Long Gui in Archylte Steppe. Control Noel during the fight and make sure he has somewhat about 800 strenght. I had over 1000 strenght in this video. Take out both of Long Gui's legs to make him fall. Raise up his damage meter to 999,9% and cast deprotect (requires saboteur). Switch to Commando and manually select the combat move called 'Attack'. Instead of attacking right away you will want to wait 2-3 seconds before stagger ends (=the yellow damage meter on top right side of the screen). When the timing is right you will easily get the 999.999 damage. If you still can't cause that amout of damage you will need to level up some more or get a synergist monster which can cast Bravega and Faithga to increase your damage even further. I recommend to have maxed out characters when trying this.