For this trophy, achieving it can be quite annoying, but it entirely depends on what you grind/where you grind.In order to obtain this trophy, you must do a preemptive strike on an enemy 100 times in a row without fail,
in order to do a preemptive strike, when an enemy appears, a clock/timer will appear at the bottom, what you need to do is use the
button to hit the enemy, if hit successfully, you will be brought into the battle with a preemptive strike, meaning you and noel both hit an enemy of your own before anything else, filling their chain gauge up halfway. Continue this 100 times in a row without fail and the trophy will be yours.
The ways you can fail is to not hit the enemies in the time and the clock will run out, automatically putting you into the battle, or not hitting them before you run into them/they run into you. I was able to obtain this whilst hunting for a rare monster in Bresha Ruins 100 AF, the reason it was easy for me here is because when the enemies spawned, they didn't run straight into you, so I suggest you find a spot where enemies tend to stand still/don't run into you so quickly, so you have more chance to ready yourself and hit them.Note for two other trophies you can gain whilst going for this one: