Season One deals with Euphemia gaining a mysterious ability called Geass, and using it to change the world so that she can return Japan to its former glory. However, her obstacles include her older sister, Second Princess Cornelia, her friend Kallen Kōzuki (whom Euphie doesn't know pilots a Knightmare known as the Guenevere), and Lelouch vi Britannia, a person whom Kallen falls in love with and appoints her as his knight.