Operation Abyss: New Tokyo Legacy

This will likely be the very last trophy you need for the Platinum. 3000 battles is a lot of battles. Try to avoid running from battles. After you've completed all of the other trophies, if you want to get this trophy as quickly as possible, go to Gakuto Sewer for the weakest enemies. If you have an Academic, cast Neo Chain to get more frequent battles. Whenever you go through a door with this spell in effect, you will be guaranteed a battle. This can be a rather long grind and, unfortunately, there is no way to tell how many battles have you fought. Consecutive battles do not count as extra battles so if the Encounter Gauge gets too high, the frequency of consecutive battles increases so you might want to escape once in a while to lower it.