In the year 2017, an exiled prince by the name of Lelouch vi Britannia started a rebellion in the newly conquered territory of Area 11, formerly known as Japan. Taking on the guise of Zero, a masked revolutionary with great intellect and skill at strategy and battlefield tactics, Lelouch would go on to form the Order of the Black Knights, a militia group made up of Japanese resistance fighters, to serve as his military arm against the Britannian Empire.
In what would later be referred to as the Japanese Insurrection, Lelouch would continually lead the Black Knights to victory after victory against Britannia, only to be held back by the infamous white knightmare frame Lancelot and its pilot, Japanese born Britannian loyalist and Lelouch's dear friend, Suzaku Kururugi. At the apex of this rebellion, Britannian Third Princess Euphemia li Britannia, who had been living and governing in Area 11 as the Sub-Viceroy under her sister Second Princess Cornelia li Britannia, would propose the Special Administrative Zone of Japan, a pocket state that while still under Britannian administration would allow the Japanese people to retain their culture and identities, as well as establish them as equals with Britannian citizens. To symbolize the unification of the two sides, Euphemia requested for Zero to support her in the SAZ.
However, just as the SAZ was to be ceremoniously brought to reality, Euphemia would apparently suffer a mental breakdown and instead order her troops to slaughter all the Japanese gathered, including women and children. The Black Knights would keep casualties to a minimal and fight off the Britannians, but the damage was done. For this deception, Zero personally slew Euphemia.
No longer willing to make amends with the Britannians, Zero would lead the Black Knights into a great battle, his goal now to eradicate Britannia's occupational forces and reestablish Japan as a nation. In this overnight battle, the Black Knights would invade the Tokyo Settlement, the nerve center of Area 11, and manage to fight their way through the Britannians with great power, with only Princess Cornelia's personal forces managing to hold them back initially. Even as Zero disappeared in the middle of the battle, leaving the Black Knights under the command of Lieutenant Colonel Kyoshiro Tohdoh, it seemed that the Japanese victory was assured, with Britannian fighting power diminishing at an alarming rate and reinforcements from the Imperial Homeland still days away from arrival. It was then that the unthinkable occurred.
Knowing that rebellion would spread throughout the Empire once the Black Knights attained victory, while Japan itself would be overrun and occupied by either the European Union or the Chinese Federation, Second Prince Schneizel el Britannia would order the enacting of Operation Nero. The systematic detonation of Japan's sakuradite reserves.
The destructive power of the islands' primary resource only ensured that Japan would cease to be. The land, and all of its inhabitants, both Japanese and Britannian, would be consumed in a collection of fire and light that encompassed an area of three hundred and thirty-seven thousand kilometers. When the dust settled, only flaming ruin remained, and all life on the islands was considered extinct.
In the midst of this, Suzaku would manage to capture his former friend Lelouch and bring him before the prince's father, the Emperor. Using the power known as Geass, which Lelouch had originally used to great effect during his rebellion, the Emperor would alter Lelouch's memories so that he would become his pawn. Living an artificial life in which Lelouch had never been exiled from Britannia, continuing to serve it willingly.
Eight years later, the Britannian Empire would be embroiled in a new conflict. With Schneizel skillfully absorbing China into Britannia through an arranged marriage between his brother First Prince Odysseus and Chairwoman Jiang Lihua (otherwise known as Tianzi), all that remained between Britannia and total world domination was its lifelong nemesis, the European Union. Thus, Britannia began a war to end all wars, directly invading European territory and conquering it one state after another.
Now a General, Lelouch would lead the Imperial war effort in the EU's North African territories. All the while supported by three Knights of the Round: Knight of Three Gino Weinberg, Knight of Six Anya Alstreim and Knight of Seven Suzaku Kururugi.
And yet, as Britannia and Europe battle each other for control of the world, a mysterious third faction moves in the shadows. Watching and waiting for the chance to reclaim its lost leader and continue what had begun eight years before...