The Empire of Britannia invaded Japan using giant robot weapons called Knightmare Frames. Japan was reduced to Area 11, an imperial colony, and its people referred to as the Elevens. At the time, Lelouch, a young Britannian boy exiled to Japan, vowed to his Japanese friend Suzaku that he would destroy Britannia.
Years later, Lelouch is a high school student who regularly skips school to play chess and gamble. When he stumbles on a terrorist group of Elevens who are caught by a Britannian task force after stealing a military secret, Lelouch is unexpectedly reunited with Suzaku, who works as a member of the Britannian military. As the rest of the task force arrives, Suzaku is shot for disobeying orders, while the military secret, a young girl, gives Lelouch the power to make anyone obey any order. Taking command of the terrorists, Lelouch adopts the alias “Zero” and begins his rebellion to crush Britannia once and for all. However, his greatest friend soon becomes one of his most troubling enemies when Suzaku becomes the pilot of Britannia’s new test model Knightmare, the Lancelot.
Note: Storyline is a bit different than the anime.