Aragami

This is easiest to obtain in versions of the game prior to v1.04, as prior to this, all kills countered as 'stealth kills'; post-patch, if a guard has detected you, you'll just be credited with a standard 'kill' if you kill them.

Regardless, for this trophy you'll need to find a pair (or more) of unaware guards standing close to each other, then kill them one after the other, chaining kills with multiple successive presses of - which should earn this trophy.

Here's a video guide, courtesy of Trophy Germany: