In the distant future, Earth is fighting a losing war with an alien race known as the Glorft. In order to save the planet, the human resistance steals a prototype giant robot from the Glorft and modifies it, renaming it Megas (Mechanized Earth Guard Attack ystem). The idea was to send Megas back to the Battle of the Last Stand, which was the last major offensive fought by humanity against the Glorft. Humanity lost that battle, but the members of the resistance believe that Megas can tip the scales and hand the Glorft a decisive defeat.
Before the plan can be executed, however, an attack by the Glorft forces the human resistance to send Megas back in time. The prototype timedrive, however, accidentally sends the now-crippled Megas (its head was blown off in the attack) all the way back to the early 20th century. Megas languishes in a New Jersey junkyard until it ends up in the hands of two slackers, Coop and Jamie, around the year 2000. Coop turns Megas into a hot rod project and names it XLR, for eXtra Large Robot.
Kiva goes back in time to retrieve Megas, and when she finds she is unable to pilot it because of Coop's modifications, she grudgingly decides to train Coop for fighting.