They've been featured in Hollywood movies, and have also been the inspiration for comic books.

And now, Japan is looking at how its legend of ninjas could boost tourism.

In the age of civil wars in the 15th century, young men were hired by samurai or feudal lords to spy, sabotage and kill.

But after more than 500 hundred years of history and myth, only a handful of grand masters hold the secrets of the deadly art of ninjutsu.

Mariko Oi went to visit two of them.

One claims to have thousands of followers, while the other explains why he has decided to let his knowledge die with him.