In a faded black-and-white photo, an old man clasps his hands, making a peculiar sign with his entwined fingers while the handle of a long sword peeks out from behind his back.

"My grandfather never lay down to sleep, he always slept sitting in a chair as if he was on the lookout. He was also good at hypnotism," recalls 55-year-old Motoharu Murai, who says he the grandson of the ninja fighter pictured in the photo.

Some ninja experts doubt Murai's assertion because the silent assassins usually operated in secrecy and never revealed their true identity, even to their families. But Murai sees his grandfather's sneaky and effective weapons and matchlock muskets as solid proof that he was indeed a ninja fighter.