Astronauts Glenn and Fuji venture to Planet X, a newly discovered world beyond Jupiter, to investigate strange occurrences. Meanwhile, Fuji's sister Haruno and her inventor boyfriend Tetsuo Torii create a sound device sold to a toy company. Upon arrival, Glenn and Fuji encounter the Xiliens, aliens seeking Earth's help to defeat "Monster Zero" and save their world. In exchange, they offer a cancer cure. As Glenn delves deeper, he falls for Ms. Namikawa and uncovers the Xiliens' sinister motives.

Monster Zero
A group of space explorers travel to Planet X to aid the Xiliens in combating an imminent alien menace, only to discover that one of their own is entangled in a secret affair with a mysterious woman whose true allegiances threaten the mission's success.