Jumper

If you are facing an enemy, the back side will be . Simply kill them with a  attack and this will unlock. Despite the achievement's name, you do not have to use your special finishing move.

Note: If you teleport behind someone or to their side, the button layout will change, so just make sure whatever side is their left, hit the corresponding button. For instance, if you are facing the left side of the screen, their back side will be .