El Shaddai: Ascension of the Metatron

I didn't have this after completing every other achievement besides the G-rank all stages ones, so I looked for a spot to farm them to finish it off. Easiest place I found was in Chapter 2- set it to Normal difficulty so the enemies don't die quite as quickly. Fight your way along and steal an Arch from the first pair of armed enemies, then you'll whack a switch and backtrack a few steps where you'll be drawn into combat with two Arch wielding enemies and this happens to be the exact spot where it gives you the guard-break tutorial. For guard break attacks to actually count toward this achievement they must actually break a guard, not just damage an enemy.

Don't even wait for these poor chumps to block. Just hit x, then wait a beat and hit x again, and you'll flip over one/both of their heads and while this is happening they usually put up a guard while you are in mid-air and as you land you'll slash them from behind, executing the guard break, often on both at once. Don't hit them when they get stunned where you can steal their weapons, just back off and let them recover, otherwise they'll just end up dying faster and you'll be able to farm less guard-breaks off them. Cake.

If one ends up dying you could just let the other one beat you to death and then make no move to execute the rapid recover which will respawn you before this fight to keep on farming as many easy guard-breaks as you want.