Achieve a streak of 100 consecutive Preemptive Strikes against enemies. When enemies appear on the field, you must quickly hit them when the Mog Clock is in the green region. If you've done it correctly the message "Great!" will appear on the screen.
You can farm these quickly by immediately pausing and selecting Retry once the battle begins, then you can hit the enemies again, and repeat. A good place to farm them is on the beach in Oerba 200 AF. There is a group of Frag Leeches and Zwerg Scandroids who are very slow moving, which makes it hard to mess up.