When starting a mission, you are given the option of choosing which cadets will take place in the mission. Some of these cadets will sometimes be highlighted with a yellow background – these cadets are "Primed" and will perform particularly well on that mission. To earn this trophy, simply only select these primed cadets to play the mission. Note that it is a good idea to primarily use Primed cadets in general, even after earning this trophy.
This trophy can naturally be earned at the same time as "Perfect Marks" and/or "Miraculous Mission", and it is convenient to earn it early in Chapter 2. See the following video guide: