Hands down the easiest way to get this is against Ifrit in Temporal Gyre (near the end of the game).
Once you go through the corridors to get to the final boss, and it is Ifrit (you can tell which boss you're facing from the checkpoint screen before going through the boss door), equip temporal orbs and, if you have it, the Star of Lachiem Ring (just speeds things up, not essential).
As soon as you go through the boss door, hold RB to dash towards the sprite. As soon as you are stood where he is, hold DOWN to crouch, and keep it held.
Ifrit will now spawn above you, and from this position none of his attacks can hurt you. Simply proceed to spam your orbs and once you kill him the achievement will unlock, assuming you didn't get hit.