Haven't seen the Ninja Assassin yet but I did see a cool episode of Weapons Masters about the Samurai sword. The reason they are so good is that they don't break. They are rated the #1 sword among most experts.
The process for making the sword is insane and very lengthy. They have a big ceremony before they make the Samurai Sword and spend months preparing the metal.
I wouldn't mind having one in my house in case of a home invasion...messy but it would get the job done.
