This is obtainable in most parts of the game, even on Brave difficulty.
The best place is either Forest Grove against the starter wolves, or Coastal Cliffs versus the bombs.
The tactic is the same. Equip the correct charm that does most damage against your opponents, the proceed to shoot with the bow. Do not bother with sword attacks.
Charged shots, especially ice can be handy here to freeze enemies if your struggling, and using dodge (LT) can also help.
To be honest, if you do this near the start, you can do it just by holding down RS in the direction you want to shoot.
Just kill 15 enemies without being hit once.