Japan, now Area 11, is under Britannian occupation. The world sees Japan as a defeated nation, but deep underground, hidden within bunkers and secret bases, Japan's true military power has been preserved.
Introduced as a Japanese high school student, Lelouch is not Britannian but a prince of Japan. His mother, Lady Marianne, who married a Britannian royal, was a beloved figure, and her assassination during Britannia's invasion drives Lelouch's desire for revenge.
Lelouch discovers a hidden lab where Japan's secret military is stored. He stumbles upon C.C., who offers him the power of Geass. Lelouch accepts, knowing this power is essential to liberate Japan.
Her name is Elizabeth VI Britannia and she is the other sister of Lelouch VI Britannia and Nunnally VI Britannia. She's often better then Lelouch and Schneizel at Chess. After her mother dies and Lelouch takes Nunnally and are forced away, she's left alone to do nothing but train by herself. After years of training, her father the emperor of Brittania sends her on errands like Cornelia and Schneizel only she doesn't use a Knightmare or an army like your other siblings. Only on her missions does she either keep the peace or she kills the problem which inevitably keeps the peace. A few years pass and she hears of Clovis's death. She attends the funeral of her disappointing brother and begins to keep track of the events in Japan as they unfold until Zero makes his presence known.