The achievement progress saves for the entire game, not just the save file, so if you have a save file with ann's power already unlocked, you can just load that save file and kill enemies with her power.

But if you dont have a savefile for that!



You will be needing to head into the Underground Base Area A, and save/overwrite your current save here.

Then head towards the left door, you will find crab enemies that respawn whenever you get into the door on the left, or go back to the right door.


In the middle of the zone, theres gonna be a few crab enemies spawning whenever you reload your savefile/teleport somewhere else and come back.

Activate your power here and kill all of the crabs in this area.
Then reload your save.

Repeat until you have the achievement.

Edit : found out that reloading your save does NOT refill your meter, however it does spawn the crabs in the middle (the ones with the red crab)

Edit 2 : Equip a weak weapon to refill your meter faster.