The achievement isn't clear about it, but you have to parry enemy attacks 10 times in the same game session for it to pop. The value seems to reset itself when you exit the game.
The easiest way to get this is to find the enemy type that has a pompadour hairstyle and is wearing a Japanese school uniform. They have an attack where they hop back then lunge forward with a kick, which is very easy to parry once you get the hang of its timing. Clear the screen of every enemy except one of those, and do it 10 times to get the achievement.