Easiest mech battle yet. Keep behind it and pummel the AI Pod with your LAW.
The hardest part of this battle, in pursuit of S-Rank is the cutscene at the end. There are actually eleven prompts by my count (three missiles to dodge, then five trees then three more sets of missiles) with no room to miss. You don't need to be completely perfect, as I got the S Rank and had 9/10 cutscene interaction bonus.
Gauge your tapping of the Triangle (or Y) button to get in between the missiles or mash it (consider changing hand position) to get ahead of them.