To earn this achievement, "Environmentalist", you'll need to earn five unique kills via the enviroment.
To do this, grab a blocking enemy by pressing and holding B. Wei will grab the guy and the enemy will try to struggle it out, but Wei is faster. While holding the guy, hold down A and run to a enviromental hazard, such as a sode machine or a nearby fan and hit B. Wei will perform the enviromental kill, in gruesome fashion, and it should count right after it's done.
I got this way early in the game, during the Night Market chase, so you shouldn't have much of a problem with this one. Good luck!