Taking place in a science-futuristic setting (where all of the characters speak alienese by sticking out their lower jaws and talking), Robiya Hime sends Luffytaro to find Mugiwaraman (not knowing they are one and the same) and stop the Universal Association of Darkness from invading the moon. Along the way, Luffytaro becomes Mugiwaraman and saves Planet Namitan by deflecting an octopus-shaped asteroid. When Luffytaro arrives at the villains' base, agent Choppasmith tells him they have gone to invade the moon. But by the time anyone gets there, it's already been destroyed by that octopus-shaped asteroid.