In the year 2079, per the Liberation Contract, scientists deemed Earth inhabitable within the next 100 years and started sending fleets to space as a way to preserve mankind.

In the year 2089, humankind came in contact with aliens…

Thus, per the Liberation Contract, the United World Alliance started development on mecha robots as a way to combat the aliens on Mars.

By the year 2157, humans have all left Earth. The world was deserted with failed mecha designs, and only one successful mech. Under the name M6-Zarbb-Q, humankind found the moon as their next home.

For the next 40 years, humankind found success on the moon, but while habitable, the lack of resources led the the Clean Up Crew and M6-Zarbb-Q back to the now deserted Earth only to find what was once deemed a failure, a nightmare to all humankind.