In Edo-period Japan, Murasame Castle houses a gigantic stone statue known as Murasame. The people lived peacefully until one stormy night, when a shining golden object fell onto the castle from the sky. Deafening shrieks arose from the castle, and the shining object is later revealed to be an alien creature who gives life to the stone statue Murasame and takes over the castle. The alien creature extends its power to four other neighboring castles, giving the daimyō lords each an evil sphere of power. The lords are taken over by the alien's evil power, and use the spheres to summon ninja armies and monsters to attack villagers. Hearing of these strange occurrences, the shogunate led by Tokugawa Ietsuna sends Takamaru, a samurai apprentice, on a secret mission to investigate the castle. As Takamaru, the player must infiltrate the four castles to defeat each castle lord, before going on to face the alien entity itself.