日本刀
"Teenage Mutant Ninja Turtles" (1987) deals with it twice. In "Ninja Sword of Nowhere", an alien spacecraft left a fragment of an alien metal, used to travel between dimensions in a mere microsecond, on Earth thousands of years ago, before a craftsman found the alien metal, forging a Japanese sword. This creates a legend of a sword which allows its owner to show up and disappear whenever he or she wishes. Even "Sword of Yurikawa" has a plot with an old Japanese sword.