When heads of state gather at the G8 summit in Japan, Guilala -- the intergalactic monster that had been banished from the earth in The X from Outer Space -- returns to ravage the Japanese countryside and threaten the world leaders. Military strikes prove futile against the beast, but a reporter learns that one rural community possesses a strange ritual that might influence the creature. Minoru Kawasaki directs this campy satire.

The story follows a Roman architect named Lucius, who is having trouble coming up with ideas. One day, he discovers a hidden tunnel underneath a spa that leads him to a modern Japanese bath house. Inspired by the innovations found there, he creates his own spa, Roma Thermae, bringing in the modern ideas to his time.