This is quite a simple trophy to obtain, as preemptive strikes are VERY helpful in this game.
I'm not sure on the /exact/ number you need, but it's not too much, nor is it as small as 10-20.In order to perform a preemptive strike on an enemy, you do the following; When an enemy appears as you're exploring, a little clock will appear at the bottom to show you this, run to the enemy BUT NOT into them, just press
so your character does an attack animation, and if you hit the enemy/any enemy, it'll say "great" and you'll initiate battle, starting off with a preemptive strike, which allows you to get first hit and get their stagger bar up halfway or so. Do this as many times as you can and it'll be yours.
Note for two other trophies you can gain whilst going for this one: *** Spoiler - click to reveal ***Also take note of the fact that when you do a preemptive strike and it gets the enemies stagger gauges up, try your best to fulfill the gauge completely to stagger them, I use AoE's to get more than one as the bars go down fast if you don't hit. If you stagger enough foes, you will be awarded the following;
*** Spoiler - click to reveal ***If you also do CONSECUTIVE preemptive strikes, meaning you every battle you get into will be with a preemptive strike and nothing else, then by the time you get this you should have the following trophy, as it's the same number basically.