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.
It's been one year since the failure of the Black Rebellion and the supposed death of Zero. Britannia has assigned Area 11 a "correctional education" status, where Elevens are made an example of by brute force, to try to prevent any future uprisings and suppress rebellious thoughts. Unsuspecting high school student Lelouch, oblivious to his rebellious past as Zero, stumbles upon a scheme on his life and the life of a mysterious woman known as C.C., who reveals to him his forgotten purpose and his "true" self. Destroying his assailants and declaring himself Zero once again, Lelouch sets out to finish what he started.
High School freshman Kōtarō Satomi wants to start a new life living alone in the tiny Room 106. That lonesome life is immediately broken by the invasion of a group of mysterious girls who all claim Room 106 belongs to them one way or another.
Kenshi Masaki is the half brother of Tenchi Masaki and used to live in Japan, that is until he was summoned to the land of Geminar. The Land of Geminar has been witness to an endless amount of wars that have been fought using Seikijin, bio-mechanical weapons controlled by a capable warrior called a Seikishi using magic power called Ahou. It is revealed that Kenshi is an amazing Seikishi and it seems someone has a reason for Kenshi to be in Geminar, but who and why are not known.
Walkure Romanze's story revolves around Takahiro Mizuno, a student studying at an academy with jousting as its main focus for sport. Takahiro acts as an advisor to the riders of the sport. Takahiro goes through each day tediously until the time of the annual competition draws near. Due to some odd circumstances, his childhood friend Mio Kisaki is enrolled into the competition. As she has never even rode a horse once in her life, Takahiro senses the fear in his friend and becomes Mio's coach.