Easily combined with:
You can get this in the first "proper" monster area, when you're given your first hunting mark, the Rogue Tomato.
The desert area you go to outside of the East Gate is full of wolves and cactites, all of which can be easily stolen from.
Simply run around the initial area, circling behind the ridge where your hunting mark is hanging out, and steal from the respawning enemies. Don't head too far out of you'll come across a dinosaur-type beast you'll want to avoid (Wild Saurian).
Remember to hit
to speed up the action (I recommend keeping it at the default 2x speed in the menu, as 4x can get you into trouble).
Every time you get close enough to a foe for it's health bar to appear, press
, choose Magicks & Technicks, Technicks, Steal and then the foe you wish to steal from.
The theft has to be successful - you'll be notified at the top left of the screen.
Unlike attacking, the Steal command does not stack, so you'll have to hammer through the
button every time.
The achievement unlocks on your 50th successful steal.
You must kill the enemies you steal from to get them to respawn