This Seeking Tech guide will show you how to unlock the Sayonara trophy in Ghost of Yotei. To do so, follow the video and text guide below:
Step 1: Unlock the Shoulder Charge or Typhoon Kick attack.
Step 2: Look for an enemy near a cliff to use Shoulder Charge or Typhoon Kick.
I got this to unlock in the Sleight of Hand quest, which has a cliff with enemies when a sniper attacks you at the end of the mission. There should be other of opportunities as well.