Special Administrative Zone Massacre

Special Administrative Zone Massacre or SAZ Incident, was a massacre carried out by the Britannian Military on the orders of Geass influenced Third Princess of Britannia, Euphemia li Britannia and the catalyst for the First Black Rebellion.

Background
The Special Administrative Zone Massacre was carried out by Britannian forces on the Japanese civilians. Prior to the incident, Princess Euphemia li Britannia formed the Special Administrative Zone as a location where Elevens would receive their rights back, albeit in a much smaller area, without any interference from the Holy Britannian Empire. Prime Minister Schneizel el Britannia, the head of government for the Empire, supported Euphemia's proposal, and allowed her to carry out the creation of the Special Administrative Zone.

Her radical proposition was met with opposition, both from the Britannian Imperial Family, who felt that their imperial hegemony was being subverted; and the Japanese themselves, who were not convinced that the zone would work, distrusted Euphemia's intentions or were resigned to live as Elevens. Zero in particular felt that Euphemia's proposal defeated the purpose of the Black Knights; acceptance would render the Black Knights powerless in their pursuit of revolution, while refusal would render the Black Knights as pariahs if the Zone was successful.

At the opening ceremony, where Euphemia was to officially grant rights back to the Elevens, Zero secretly confronts Euphemia at her office. Hoping to make himself a martyr, Zero intended to force Euphemia into shooting him. However, Euphemia successfully convinces Zero to follow through with her plan, and the two came close to carrying it out. Unfortunately, on an offhand joke, Zero accidentally Geassed Euphemia into shooting all Japanese at the Special Administratve Zone, forcing Zero to murder Euphemia personally.

The Battle
Euphemia (accidentally Geassed by Zero) runs to the podium and asks the Japanese people to kill themselves. When she realizes that they won't do it, she decides to shoot them herself and issues an order to all Britannian forces to slaughter every last Japanese in the area. Andreas Darlton tries to confront her but ends up getting shot as well.

Suzaku, who was unconscious due to coming in contact with C.C., tries to stop the soldiers but because he's also Japanese, they try to kill him as well. Feeling disturbed by the entire incident, Lelouch tries to leave and manages to pass Darlton unscratched because the man is wounded. Inside Gawain, C.C. is surprised about the incident but Lelouch tells her that this is not his doing. Upon seeing Lelouch's active Geass eye, C.C. then understands what happened. Zero now realizes that the only thing they can do is to make the most out of the incident. After destroying Britannian planes, he issues orders to the Black Knights stating that Euphemia has become their enemy and the Special Administrative Zone of Japan was just a trap. He orders the group to destroy the Britannian army and save the Japanese. Lelouch then cries and gives his final order: Find and kill Princess Euphemia.

All the Japanese, including Kallen, are outraged and agree to assassinate Euphemia. Guren Nishiki and Tohdoh's Zangetsu frame prove more than a match for all the Britannian Knightmares present. While trying to stop a frame from shooting at civilian, Kallen realizes that the pilot is none other than Euphemia. Kallen charges, but Zero already arrives on the scene with Gawain. He dismantles Euphemia's frame using Slash Harken and Euphemia ejects. Despite this, she picks up an automatic rifle to shoot at Gawain and Guren Nishiki. Eventually she runs out of ammunition, so Zero comes out of Gawain and proceeds to approach Euphemia. Suzaku is frantically looking for Euphemia and finally finds her, directly in front of Zero. Euphemia asks Lelouch to set up the Special Administration Zone of Japan along with her, though she is puzzled at the word "Japan" due to Lelouch's previous order to kill them. Zero says that he would have liked to have done that, but that it is impossible now and instead shoots her in the abdominal region, mortally wounding her. Suzaku is driven completely berserk and charges at the Gawain, however, the Gawain escapes and Suzaku rescues Euphemia and brings her to the Avalon. Unfortunately, it is too late, for by the time he gets to the Avalon, Euphemia's wound is so grave that she dies while being treated by paramedics.

Aftermath
After the incident, Zero, overwhelmed by guilt, decided to stick back to his initial plan and rallying the Japanese at the stadium, thus declaring the formation of United States of Japan. Insurgency ensued all across Area 11, with Japanese hunting down every Britannians they could find, while Zero personally commenced an unsuccessful Assault on Tokyo Settlement. V.V. who was observing behind the scenes used the conflict as an opportunity to bring down Zero by telling Suzaku the truth whom the latter reveals the truth in front of Kallen as well therefore bringing an end to Zero's reign.

Also, Chinese Federation countries including Taiwan, Korea, China, Thailand, and Vietnam declare war on Britannia. Later, Nunnally vi Britannia tried to reestablish the Special Administrative Zone but failed because of the lack of trust as a result of the previous failure conducted by Euphemia li Britannia. This worked as an advantage for Zero, because he formed a plan of exiling himself out of Japan in return of the reestablishment of the SAZ. His true plan was to exile the Japanese people along with him that had attended by disguising them all as Zero. Schneizel would later inform the Black Knights that Zero had used his Geass to make Euphemia carry out the massacre (which was technically true, except that Zero had done so by accident), presenting an audio recording of Zero admitting it to Suzaku. This ultimately played a major part in the decision of the Black Knights to betray Zero (though for the most part it was a fear of Geass).