Mars

Mars is the fourth closest planet to the sun, and the fourth and final inner planet of the Solar System. It is occasionally referenced or makes appearances in Toho's Godzilla series and other Tokusatsu movies. The popularity of space movies in the latter half of the twentieth century meant that other film companies, such as Daiei and Shochiku also made films that were at least partially set on Mars.

The Mysterians
The Mysterians are known to have been inhabiting Mars prior to the events of The Mysterians due to the destruction of their home planet, but travel to Earth to mount an invasion because Mars yields too few resources to sustain their population.

Invasion of Astro-Monster
In this film, the Xiliens' home planet, Planet X, is mentioned to be between the orbits of Mars and Jupiter. However, the proximity of Jupiter in the Planet X sky suggests that Planet X is closer to the latter planet than the former.

Godzilla: Monster of Monsters
Mars is the second planet visited by Godzilla and Mothra in the game. Here, Mars is shown to be quite unlike the way it is in real life. Volcano levels are extremely common on the planet. In addition, Mothra and Godzilla must fight both Moguera and Gezora, who have followed them from Earth, but must also fight Varan.