Anyone that has ever seen a ninja movie know that ninjas are stealthy. They sneak up on their foes and dispatch them with one blow. You can't kill a pirate with one blow. Anybody with a pegleg, a hook for a hand and an eyepatch who is still fighting ain't going down easy.
Ninja sneaks up hits pirate with shrukien. Pirate laughs, ninja kisses element of surprise and his *** goodbye.
Arrgh, you call that a deathblow, have at ye now...