遥远未来，世界人口数在迎来巅峰后，开始呈现下降的趋势。人类为了让物种繁荣存续，制作出管理生态系的AI，并执行「人类多样化实验」。常人、兽人、魔族等经过遗传因子改造诞生的「多样人种」，在环绕高壁的生活圈之中，打造出被称作「CLUSTA」的「多样城镇」。有着丰富人口的「CLUSTA」，在各地都有不同的文化发展以及适合在地生活的人类居住。
为了不面临灭绝，人们都在AI的管理下度日──。

Tout ce qu'il sait, c'est qu'il vient d'ailleurs. Jusqu'où la poursuite de ses origines va le mener ?

The side story takes place in 2017 a.t.b., between the rise of the “Black Knights” organization and the return of the supposedly "dead" Zero. The setting is in Europe, where the European Union (E.U.) allied nations are being invaded by the overwhelming forces of the Holy Britannian Empire. On the verge of defeat, the E.U. army forms a special unit known as “W-0″, of which a young pilot named Akito Hyuga is a member. Leila Malkal , a former Britannian Aristocrat comes to the E.U.'s aid, commanding the “Wyvern” Knightmare corps comprised of Japanese teenagers. They recklessly plunge into a battlefield, where the survival rate is extremely low, at about 5% only. They fight for their freedom and for a "home" to which they can return.

The war between Euro Britannia and the European Union continues. New orders are given to the W-0 Unit. To land in the middle of the enemy territory as a diversion. The pilots of the W-0 Unit consist only of the commanding officer, Leila, the only surviving Japanese from their last battle, Akito, and the three that escaped from the Eleven ghettos and lived in the underworld, Ryou, Yukiya, and Ayano. With everyone holding their respective expectations, the operation moves forward. On the other side in Euro Britannia, Shin, who made his benefactor commit suicide with the mysterious power of “Geass”, is appointed the leader of the Knights of St. Michael. As Shin steadily advances for the sake of his own ambition, he and his subordinates in the Ashura squad are given orders to deploy. The one that lives in order to fight, and the one that fights in order to live.

The world is at war. Lelouch Lamperouge, an exiled prince, encounters a strange girl known as C.C., who gifts him with a great power. With this ability, Lelouch can get anyone to do as he wills. But the power of Geass: is it a blessing…or a curse?