Crimson Razor (Ex)
At 8th level, you gain the ability to unerringly strike at the vitals of your foes. Once per day, you may declare one melee attack a crimson razor. You must do so before you make the attack roll; if the attack misses, you still lose that use. If the attack is successful, than it is automatically a critical hit. You cannot declare an attack both a crimson slash and a crimson razor. You gain an additional daily use of the crimson razor ability at each subsequent level.
For this, you will probably want to list the levels.