A substory pretty early in the game will introduce you to the Sujidex (I believe during Chapter 4 it shows up).
This is basically a Pokedex, if you know Pokemon! It lists eveyr single enemy you encounter, and for this cheevo you'll need to encounter 200 of the 252 sujimon. It may sound like a tall task, but it's really not. Just after you do the substory, you can keep checking your progress via the main menu. It should occur over time, probably near the end of your playthrough.
This article provides more info on the substory itself:
https://samurai-gamers.com/yakuza-like-a-dragon/chapter-4-th...This article shows a list of all 252 sujimon. WATCH OUT FOR SPOILERS, THIS FEATURES A LOT OF SPOILERS SO READ AT YOUR OWN RISK. I'D RECOMMEND NOT LOOKING AT THIS UNTIL AFTER COMPLETING THE MAIN STORY!!!