Use Milla and use the Minimum damage skill.
Just go to a weak monster area and set all characters on autoprotect so they don't attack.
Link one of them to make him fight monsters and only leave one alive then unlink him.
The trick is to use Milla's binding sphere arte and let it do damage. Attack with you sword when it's about to finish and end your combo with another binding sphere. Stop attacking so the AC counter resets and allow you to slash again, ending with binding sphere.
Rince and repeat ^^