The Empire of Britannia has invaded Japan using giant robot weapons called Knightmare Frames. Japan is now referred to as Area 11, and its people the 11's. A Britannian who was living in Japan at the time, Lelouch, vowed to his Japanese friend Suzaku that he'd destroy Britannia. Years later, Lelouch is in high school, but regularly skips out of school to go play chess and gamble on himself. One day, he stumbles on terrorists 11's who've stolen a military secret and is caught by a member of the Britannian task force sent after them, who is Suzaku. As the rest of the squad arrives, Suzaku is shot for disobeying orders, while the military secret, a young girl, gives Lelouch the power of Geass, which makes anyone obey any order. While Suzaku is secretly made the pilot of Britannia's brand new prototype Knightmare, Lancelot, Lelouch becomes the masked Zero to lead the rebellion to destroy Britannia once and for all.
Eleven years after the introduction of internet-connected, augmented reality eyeglasses and visors, Yoko Okonogi moves with her family to Daikoku City, the technological center of the emerging half-virtual world. Yoko joins her grandmother's "investigation agency" comprised of children equipped with virtual tools and powerful metatags. She quickly crosses paths with Yoko Amasawa, an expert hacker of the virtual environment, as Amasawa relentlessly seeks to "unlock" the mystery of a computer virus that emerges from an inaccessible corrupted space.