The year is 2017 of the Imperial Calendar and the former island nation of Japan has risen once more. Following the infamous Special Administrative Zone Massacre, a rebel organization called the Black Knights are lead into battle against the Britannians by their masked revolutionary leader, Zero. This incident, called the Black Rebellion, sweeps across the colony of Area 11 and it seems that Japanese independence is imminent, until Zero leaves the battlefield.
In truth, the man behind the mask is an exiled prince of Britannia named Lelouch vi Britannia who goes off to rescue his younger sister Nunnally. Due to his absence, moral among the Black Knights begins to falter, until two unknowns come to assist the rebels. These two are Rai Sumeragi and Lucian, two escapees from a Geass Research Facility known as the Geass Order. The duo assist in not only saving Lelouch, but in defeating the Britannian forces in Area 11 and formerly establishing an independent nation.
However, Lucian is soon revealed to be Lelouch's long lost twin brother and Rai is revealed to be a traitor, resulting in the fall of the short lived United States of Japan.