El Shaddai: Ascension of the Metatron

This is rather self-explanatory. It popped for me around the end of Chapter 7 on normal difficulty. I was not running past any enemies and searching every nook and cranny, so your results may vary slightly.

edit: The kill count for this achievement, as well as weapon steals, etc, are tallied across all saves/retries and totaled up independently of your save files, and I did a fair amount of exploring looking for secrets which probably resulting in my death, and having to fight parts several times, as most people seem to get this towards the end of their playthrough. :p