Stellar Blade

In the Attack skill tree, in the top left, is a skill called Ambush, which allows you to takedown most enemies with a button prompt, provided you attack them from directly behind them and they don't know you're there.

Don’t worry about sneaking, though, as you can sprint full speed at an enemy and perform an Ambush. The only thing you need to make sure of is that you run directly behind them (not at an angle). Also, if they’re in a group, other enemies who see you might alert the enemy with your back to it - but not all the time. So just be aware of both of those points.

Still, you should likely get the ‘Silent Executioner’ without trying, so fear not - I unlocked it well before finishing the Altess Levoire, which is super early in the game. Regardless of the trophy, you should unlock this move ASAP, as it’s a super powerful and effective move.