Aragami
40 Achievements
EA Play
Their own medicine
Use an explosive light to kill a guard
How to unlock the Their own medicine achievement in Aragami - Definitive Guide
In many of the game's chapters, you'll encounter floating spheres of light. Approach too close to these and they'll attempt to attach themselves to Aragami, then detonate within a few seconds. However, if you can find and attempt to attack a guard in their period before the explosion, you'll use this explosion against the guard and instantly kill them - earning this trophy as you do so.
Here's a video guide, courtesy of Trophy Germany: