Make a party with Yuri, Karol ( he must be in the party ) Judith and Rita.
Make Rita your control character and set out your artes with "Violent Pain". When the monster goes into "Over Limit" he starts digging into the ground, now your able to take a shot and hit him.
What to do? Start your Over Limit and spam the Violent Pain attacks, do this 1 time and the hits will count toward, just finish the battle and achievements pops after the battle.