In 2785, full-scale war breaks out on Earth over the various nations' rights to extraplanetary resources. This war ravages the Earth's environment, forcing humanity to flee underground. It also sees the creation of the M.R.S. (Machine manufacture Research and development System), an automated manufacturing and battle system designed to allow wars to take place without actual human participation. Unfortunately, within five years of humanity's flight underground, M.R.S. has completely taken control of the Earth's surface, and the first exploratory group from humanity's underground Shelters is annihilated.
Not long after this first exploratory mission, the M.R.S. system discovers the Absolute Dimensional Barrier technology and eventually refines it into the Dimensional Absolute Barrier Shield; it uses its SMD series of warplanes to test and perfect the system. Unfortunately, the prototype unit, SMD-00x, disappears after activating the barrier for the first time, and though M.R.S. is eventually able to establish contact with the dimensional void into which SMD-00x disappeared, it's never actually able to find the ship again.
Nevertheless, the system continues developing the SMD series, creating smaller, more capable craft such as the SMD-24-0x "Samidare", which is piloted by a humanoid control unit, C-22, and the final unit, SMD-31-FX "Gesshoku", whose control unit, C-23, possesses an advanced, self-aware AI.