New Imperial Japanese Army soldier

In November of 1941, a pair of schoolchildren in rural Hokkaido found a cave opened up by an earthquake which led to a chamber with a strange artifact that they activated opening a gateway. They informed their father, who was a shore officer in the Imperial Japanese Navy about this who sent men to investigate. On the other side of the wormhole was a network of tunnels some 800 meters below the surface of Mars as well as a strange set of machines which served as generators, life support mechanisms and smelters that broke down rock into it's component atoms. The IJN secured the location and began exploring and mining the metal rich soil and collecting ingots to feed Japan's industry, providing the Empire of the Rising Sun with some 11,000,000 tonnes of iron ore, 1,800,000 tonnes of steel, 700,000 tonnes of aluminum and 125,000 tonnes of copper and more which did benefit japanese industry, but it was still effectively a drop in the bucket. Had this been discovered a couple of years or even a few months earlier, war might have been averted, but as things were in motion the US was attacked drawing the Japanese Empire.

Their operations remained secret for about five months until the IJA got wind of it and pushed for involvement. Eventually negotiations between the two fractious services of the Empire's military were made and the IJA was given some access to the Mars Gate in exchange for a greater degree of cooperation. In 1942 manufacturing began on Mars, making use of raw materials and power on site as well as experiments in growing plants as large numbers of slave laborers were imported and managed by IJA handlers. In 1943 farming began as grow lights were set up along tunnel roofs and human waste was used to make usable soil for cultivation under grow lights. Tens of thousands of slaves were worked to death and their corpses were used to feed their fellows and contribute to the soil production efforts, though their efforts would yield an increasing percentage of calories. By 1944 as the fortunes of war for Japan continued to turn for the ill, a plan was enacted as a contingency against US invasion as a large number of Japanese civilians (as well as an increased number of Romusha slave laborers, especially female ones from China) were moved through the gate, a disproportionate number of which were young women as well as a younger member of the Imperial Family (which the military very carefully avoided informing the Emperor about) while burning records and manufacturing fake ones. After the atomic bombs fell in 1945, the IJA leadership enacted the last stage of their plan, forcing through the remaining people at the station and blowing up the earth side of the gate. Thus some 253,000 Japanese civilians, 18,000 IJN and IJA personnel, 138,000 foreign born slave workers and 600 skilled foreigners (including, in a situation which was at best a awkward a handful of Germans and a small number of Jewish refugees from Europe) were left on the Red Planet.

The military leadership in conjunction with some civilian technocrats and business owners formed a new provisional government with the young princess crowned Empress as it's formal ruler. Their population growth would spike in the aftermath of the war as fierce pro-natalist policies were put into effect that would see a major baby boom over the next two decades and would remain high afterwards. The new Zaibatsu would push forward expansion through the tunnels, built new machines and begin research and development. Some of the excesses of brutality against the Romusha labor force were cut back due to the pressing need for manpower and the lack of replacements, but they would continue to live in squallor motivated by fear of their masters, minor rewards in improved rations and alcohol and the hope of entering the Second Class of citizenship that had it's origins in the 600 skilled foreigners. But even for those of pure Japanese dissent the life was still a hard one. The workload was heavy, luxuries were scarce and the laws were draconian. Only through military service or by developing one's technical skills could one advance. Research and development was made and the surface of the planet explored as they made their plans. Standards of living would improved slowly over time on the whole (by 2000 most Martian Japanese families could afford meat or fish at least once a weak along with tea and sake, could go out to see movies or buy manga and lived in multi-room quarters with running water, electricity and a radio with televisions being available to the middle class and even Romusha slaves had clean bunks and sufficient calories if well behaved), but most of the efforts of this society were expended towards developing industrial capacity.

It was only in 1997 that the first tier of surface settlements was detected was detected by the Mars Global Surveyor on Hesperia Planum, which also detected the launch of their first spacecraft in 1999 and their RADAR. When the Curiosity Probe touched down nearby the settlement with a first contact payload it came as a considerable surprise to the people of the Earth when a pair of soldiers came up in an electric rover and picked up the probe and the explanation which was eventually given to the people of the earth of the Empire of Shin-Nippon with it's 3.5 million subjects.

New Imperial Japanese Army combat spacesuits were designed with elements borne of a romantic streak. The Nylon, Fiberglass and Steel body armor designed for their use was intended to invoke the image of the Samurai, though it had proven itself resistant to shrapnel and pistol fire in tests. They are armed with a Type-21 Ikuta Rifle (a 6.5x40mm assault rifle based off a couple of StG-44s and Type-99 light machine guns replacing the older Arisaka and Type-5 Semi Automatic rifles that were brought over from earth), Type-35 Pistols (not shown, basically a refined Nambu Type-14), hand grenades and a Katana (a few of which were made by swordsmiths, but most were mass produced affairs) along with rocket launchers, mortars and other squad and platoon level weapon. The NIJA at this point did not do much and had little practice with only the suppression of a few Romusha riots in it's 58 years and drills. Even so it was deemed important to maintain a standing army of some 50,000 soldiers to keep up a strong marshal spirit among the population and prepare for a dreamed of day in which they would retake the earth.

Needless to say the discovery of the Empire of Shin-Nippon caused a stur on earth, which ranged from some Far Right terrorist acts in Japan to a rise of anti-japanese sentiment in Korea and China to the publication of several comics, movies, video games, anime and manga series about this development. This was particularly problematic for President Bush with the War on Terror and who now had to deal with the prospect of this newly revealed nation elsewhere in the Solar System. This did however see an increased degree of funding for Space Programs by the US, EU, China, Russia and Japan. In 2010 President Obama finalized negotiations on an international mission to Mars and announced the construction of the Ares. The Ares took five years to build even with the assistance of moon made structural materials, carried 48 astronauts, diplomats and anthropologists to the red planet and if worse came to worse carried several missiles, two CWIS turrets and four tactical nuclear weapons. It was launched in 2016 and arrived in 2017, met by a fleet of NIJN gunboats before sending down it's landing parties to begin negotiations, which were met by a formation of NIJA soldiers. Relations were difused somewhat for the time being and some concessions were made by the Empire (namely that it had exclusive domain over the entirety of mars even thought it had effective control over only an area a couple hundred kilometers across). Even so, the military leadership still maintained it's ambitions.

Please note: I am not condoning the real world Empire of Japan.