Mars is a human colony world colonized by the Union Aerospace Company. Once on Mars, said company found tears in reality to what humans understand to be Hell, a section of the dead universe formed by human thought process.
Once a world populated by martians, they met their demise after harvesting of argent energy caused them to be invaded by a force from Hell. To push this force back, they pooled their souls into a device known as the "Soul Cube", the combined might of their souls able to absorb the energy of a demon's soul and use it against them, no matter how powerful the demon. The Demons were ultimately pushed back by the Martians into their hell, which served as a nexus of sorts between universes.
When the Union Aerospace Company tried colonizing millenia after the Martian's extinction and started harvesting the Argent Energy from Hell, the demons once again began to invade, with only a mysterious figure of legend known as the "Doom Slayer" between them and total domination of the human race.
Due to this conflict going on, The Jupiter Empire has kept their distance between Mars and Earth.