Chained Echoes

This achivement will come naturally through normal playthrough.
In my case it popped as i was finishing the first region Rohlan Fields after 6 or 7 hours into the game.

If for whatever reason you are looking to farm this to rush the unlock.... Enemies respawn when you leave and return to an area so you can theoretically find a weak group and kill away for the unlock.

Just keep fighting and winning enough battles, and it will pop immediately.