Taitei no Ken

A wandering warrior named Yorozu Genkurou carries a massive sword that makes him formidable in battle. While traveling through a dark forest, he witnesses what appears to be a spaceship crashing. Soon after, he is repeatedly attacked by unusual ninjas and ambitious fighters. He eventually discovers that these attackers are aliens who have arrived on Earth to retrieve three artifacts made of Orichalcum, a substance with strong mystical properties. His sword is one of these artifacts. A conflict ensues.