12.09.2025
I've unlocked it by starting a new game and doing every mission with a takedown in one sitting.
From the first mission, instead of using guns, use takedowns if you can. When I did Burke's first kill mission, I got the achievement. I've died many times before and had to redo many missions, but I got the achievement.
If you keep doing takedowns in every mission without quitting the game, you should unlock it.
If it helps, first, I've deleted my save file folder before I started a new game.
It doesn't matter if you do a stealth takedown or a brutal one, as long as it's a takedown.