Don't worry about this too much. You will unlock this naturally if you don't skip any enemies on your path. The trophy should unlock during
CHAPTER 3-1 while playing as Parker Luciani in Terragrigia with alongside Jessica Sherawat.
At the end of the chapter you will have to wait for the elevator to arrive. This is where you get ambushed by a lot of
HUNTERS, I mean a lot. Call the elevator and run immediately back from where you entered the room. Camp here and the Hunters will come for you from only one direction, mostly in packs of three.
That's where it unlocked for me (fresh game no NG+). If it doesn't unlock for you
simply restart checkpoint. The kills are cumulative. Just keep killing until it unlocks.
You'll also unlock the
PC356 pistol with 5 slots to use for the campaign with this challenge.
Hope this helps a little.
