The Purist faction within the Britannian Army scapegoats Suzaku for Clovis' death, planning to use him as an excuse to rid the army of Honorary Britannians. Lelouch concocts a plan to save his childhood friend, with some help from Kallen and Kaname Ohgi, leader of Kallen's resistance group. Announcing himself publicly as Zero, Lelouch declares it was he who killed Clovis, and uses his power on Jeremiah Gottwald to force him to assist in Suzaku's rescue. In private, Lelouch offers Suzaku the opportunity to turn against Britannia for falsely accusing him, but Suzaku refuses, wishing to change the Empire from within.

Cornelia and the Britannian Army heads to Narita, hoping to destroy the remnants of the Japan Liberation Front. Lelouch has his Knights follow her in the hope of capturing her alive so he can question her about his mother's death. As the Britannian forces close in on the Front's headquarters, Kallen utilizes her new Knightmare Frame, the Guren Mk-II, to cause a massive landslide that takes out much of the Britannian forces.

C.C. departs as a messenger to the Chinese Federation and Milly has a marriage interview with Lloyd Asplund, creator of the Lancelot. Mao returns to kidnap Lelouch's sister, Nunnally, and holds her hostage in the Ashford Academy sewers. Lelouch and Suzaku work together to rescue her, with Suzaku's physical adeptness and the clever use of Lelouch's Geass proving to be beyond Mao's planning. Before he can be arrested, Mao reveals that Suzaku killed his own father, and in return Lelouch silences him with his power. C.C. returns to the campus and finally ends Mao's life as Suzaku crumbles to the ground, confronted with his actions after years of secrecy.

Lelouch's strategies give the Black Knights and their allies the upper hand in their battle against the Britannian Army. As riots break out through the country, the Black Knights take over the Ashford Academy as their headquarters, and the students are spared on Lelouch's orders. An enraged Suzaku, now informed of Zero's identity by a mysterious young boy named V.V., pursues Lelouch for revenge, which Cornelia also covets.

Lelouch deduces the nature of Rolo's Geass and convinces Rolo to spare him; in return, he will hand over C.C. Li Xingke confronts the Eunuch Gao Hai and kills him to take command of the consulate. As the deadline approaches, Guilford prepares to execute the captured Black Knights, until Zero appears, challenging him to a duel. Using the same strategy from the Black Rebellion, he collapses the portion of the settlement they are standing on, causing confusion amongst the Britannian military as they are dumped into Chinese territory. While Kallen and the Black Knights rescue the prisoners, Rolo appears in the Vincent to kill Lelouch for his betrayal. However, Lelouch takes a bullet meant for Rolo, giving the youth pause. Lelouch plays on his insecurities about his future and sibling relationship, convincing him to join his cause.

The Black Knights question Lelouch's decision, and the Britannian Army remains wary of his intentions. In a private conversation with Suzaku, Gino Weinberg, Anya Alstreim, Lloyd Apslund, Cécile Croomy, and Miss Romeyer, Zero requests he be exiled from Area 11 in exchange for delivering one million participants. The Britannians think he is abandoning them to ensure his own safety, and accept. At the opening ceremony, Zero asks Suzaku what it means to be Japanese, to which the Knight of Seven replies it is a shared heart. When every participating Eleven dresses as Zero on cue, Suzaku has no choice but to exile all one million "Zeroes", unwilling to start another massacre in the face of their peaceful resistance.

Rolo admits to causing Shirley's death; rather than blame Rolo, Lelouch blames the existence of Geass itself. In retaliation, he mounts an assault on the Geass Directorate, slaughtering every man, woman, and child within the stronghold. V.V. pilots the Siegfried in an effort to stop the Black Knights, but is defeated by both Lelouch and Cornelia. He escapes to the Thought Elevator, where Charles awaits, and when Lelouch follows he is transported to the Sword of Akasha. Meanwhile, Kallen and Nunnally discuss Lelouch. They are interupted by Suzaku, who, despite having been told that Shirley's death was a suicide, decides to interrogate Kallen using Refrain, in order to confirm his suspicion that Lelouch has become Zero again.

As the Emperor prepares to begin Ragnarok, Lelouch and Suzaku head to Kaminejima to face him. No longer restrained by his notions of wrong methods being meaningless, Suzaku strikes a deal with Schneizel to become the Knight of One, in exchange for assassinating the Emperor. Lelouch, using his Geass to its full potential, compels much of the Britannian military on the island to follow his commands. Meanwhile, the leaders of the Black Knights decide to declare Zero dead, as the truth will be far more difficult to swallow, but their story is doubted by others. Anya's mind is taken over by Marianne, who restores C.C.'s memories. The two begin to put their own plans into motion. At Kaminejima, Suzaku is held at bay by Bismarck, while Lelouch marches into the Sword of Akasha, through the Thought Elevator, unopposed. Knowing he cannot kill his father, Lelouch destroys the entrance, planning to seal them both inside for eternity.

Lelouch and Suzaku fight for the sake of their promise, the Zero Requiem. Suzaku battles Kallen, while Lelouch confronts Nunnally, his biggest and dearest enemy.