Hi-Fi RUSH

You first learn how to parry when you in the facility during Chapter 3 "Track 3: Trial By (Volcanie) Fire", after the tutorial on parrying various enemies, you will come across another sword robot by itself as you progress the level which you can parry its sword attacks on the same robot to 200 perfect parries

You unlock the Parry ability near the end of Stage 3 Research & Development. After a brief tutorial on how to use parry, you'll move through a lobby and into a "live" combat room where you'll find one lone swordsman. He's a perfect adversary to grind out the full 200 perfect parry's if you wanted to get the achievement out the way.

I found the best method was just to keep pressing in time with the beat and in most cases his attack was parried perfectly. If you die you'll spawn outside the same room to attempt this as many times as you like. It took me a few seconds to get the 15 parries and a further 10 minutes to get the full 200.

Obviously this achievement can be done anywhere throughout the game, but this was the first ideal scenario to get it finished.

Apologies on the video quality my capture card crashed during the R&D stage

You are taught to parry in level 3, Trail by Volcanic Fire, across multiple tutorials. The final tutorial pits you against a singular enemy with a sword. It only has two basic moves, attacking with one swing of its sword each time. This makes it super easy to time and perfectly parry its attacks. You can grind this out here if you don't damage the enemy. So feel free to return here after completing the game, if you haven't unlocked it yet, for an easy grind!