This trophy is titled "Squirrel Power!" and it's for landing Makoto's distortion "Particle Flare" with all level 3 attacks. These attacks have 3 levels, all of which depend on how long you hold the D button. It starts at one and fills up at a moderate pace, then decreases back to the start if you don't release D at the peak. You can see the meter just above the distortion meter. The first level is the easiest to hit 3 with, then the box becomes smaller with the next move and the one after that. All I can say is practice the timing and watch the bar at the bottom of the screen instead of what your character is doing. It's fairly easy to get a feel for the time, so don't stress too much.
Some simple facts about this. You do the move by putting in Two Quarter Circles forward + D (X on default controls). You then hold D to charge up the move. The meter will fill and close to the end you want to release, then hold it again for the next part. You'll need 50 heat each time you want to attempt this. Build that by attacking foes or using a second controller to attack you and instant block their attacks. As with most of these trophies, your best bet is to do it in local/online versus modes so the opponent doesn't attack, though this one is manageable against the AI.