Easiest level to obtain this on is level 3 "the hunt for answers" after you follow the messenger and go up the elevator you will have a cutscene take place in front of the ruined home. From here make your way to the next level in front of the large white building that you need to sneak into.
On the left hand side there is an archer on the roof teleport onto it and stealth kill him from the right side this will cause his body to fall off the roof. below him are 2 guards holding a door, 2 walking back and forth and 1 in the back watching your direction. One the body drops down in front of them the alarm will go off and they will start to come closer to the body.
Throw both of your Kunai down (this achievement does not need to be done with a singular kunai) wait for 4 of the patroling guards to have the large symbol above their head. Once this is visable hold your ablitiy button to kill 4 at the same time.
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