In the time of the Edo Period, an evil alien from parts unknown called Demon Scorpion plots to kill Tokugawa and ravage the land with the help of his Scorpion Ninja Army and his giant demon monsters. However, the shogunate summons his ninja bodyguards the Mitsurugi siblings, Ginga, Suisei and Gekko to combat this threat. When a giant demon appears and terrorizes the people, the three ninjas leap into the air and cross their swords to become the armored warrior Mitsurugi.