Battle of Mt. Fuji

The Battle of Mt. Fuji was the decisive battle between the Holy Britannian Empire led by Emperor Lelouch vi Britannia and the United Federation of Nations with former Britannian prince Schneizel el Britannia leading the The Order of the Black Knights that had escaped from Japan after the reconquest of the mainland. The battle was the second phase of the Zero Requiem, and was the most destructive battle in all of the world. The battle was waged for the control of the superweapon called the Damocles which was armed with a arsenal of F.L.E.I.J.A. warheads, to determine who would control the entire world. It is the final battle of Code Geass R2 and the final battle of the original series.

Background
After Lelouch's actions at the Tokyo Settlement, which resulted in Lelouch taking all the UFN representatives hostage, the Sky Fortress Damocles is first unveiled, obliterating Britannia's capital city, Pendragon, with a F.L.E.I.J.A. strike.

To Lelouch and Suzaku's surprise, Schneizel reveals that Nunnally is alive and well. However, she declares herself to be Lelouch and Suzaku's enemy, leaving Lelouch despaired. Nevertheless, the Damocles advanced through Japan on its plotted course to the Yellow Sea, from where it would ascend into orbit and into a position to target the whole world at once, Schneizel intending to use the Fortress to subjugate the entire world. However, Lelouch decided to take the fight to Schneizel, bringing the full might of the Britannian Military onto the Damocles with its escorts, including The Black Knights, as it was passing over Mt. Fuji, Japan, Before the battle, Lelouch addressed his entire Royal Guards and his other Forces, warning them that control of the Earth itself was at stake,

The Battle
The battle begins with Schneizel extending the UFN forces outwards to prevent Lelouch from outflanking him. Lelouch attempts to make several false openings, but Schneizel sees through the various attempts to get him to attack. Both the UFN forces and the Britannian military were locked in a stalemate until Schneizel found an opening that allows the Black Knights to advance right through the center line where the Avalon is positioned, forcing Lelouch to keep drawing back. The highly skilled Black Knights were able to pierce right through the frontlines to get to the Avalon, forcing Lelouch to emply a special backup plan. As the creation of the F.L.E.I.J.A. Eliminator was underway, Lelouch remotely detonated the Mt. Fuji Sakuradite mines, resulting in a volcanic eruption that decimated much of the Black Knights' forces, including the flagship Ikaruga, which was shot down near the mountain and was subsequently evacuated. However, in causing the eruption, Lelouch sacrificed his own ground forces as well. With Schneizel's forces cut in half, the commander was forced to deploy the F.L.E.I.J.A. warheads onto the Britannian ranks, the battle turning into wholesale slaughter. After seeing that F.L.E.I.J.A.'s detonation could not be prevented by destroying the warhead, Lelouch orders all his units to spread their ranks and fall back, including the Avalon - even with its Blaze Luminous shielding, it was too dangerous to expose his flagship. Schneizel also decided not to target Avalon, as there were hostages on board. For the time being, Lelouch ordered his forces to attack in waves in an attempt to force Damocles to exhaust its firepower.

Once the F.L.E.I.J.A. Eliminator was complete, Lelouch changes tactics to charge right into the Damocles with the hostages onboard. The remnants of the Black Knights who managed to survive the eruption regroup to make a counterattack against the Avalon. Suzaku, in his Lancelot Albion, manages to defeat some of the Black Knights, including Kyoshiro Tohdoh and Shinichirō Tamaki. However, the Avalon is also damaged and forced to land, with Lelouch leaving the ship aboard his Shinkirō, already fitted with the F.L.E.I.J.A. Eliminator. As he does, however, the Black Knights' boarding party, led by Li Xingke aboard his Shen Hu, boards the Avalon, proceeding to rescue the hostages. After the F.L.E.I.J.A. was disabled mid-flight, Lelouch creates an opening in Damocles's Blaze Luminous, allowing himself and Suzaku to board the station, Gino trailing after them and destroying the Shinkirō, before being defeated by Suzaku. Suzaku, however, challenges Kallen on her Guren S.E.I.T.E.N. in a duel outside the Damocles. As a result, the Lancelot Albion was utterly destroyed and the Guren was severely damaged, Suzaku being supposedly killed and Kallen saved by Gino. Meanwhile, Jeremiah Gottwald defeats Anya Alstreim aboard her Mordred, but uses his Geass Canceler on her instead of killing her.

When aboard, Lelouch proceeds to take the majority of the Damocles' personnel under his Geass. Afterwards, he fools Schneizel into believing that he was on the command deck, surprising Schneizel when he arrives into his almost-launched shuttle instead. Lelouch uses his Geass to subdue Schneizel, making him serve Zero.

One obstacle is then left in Lelouch's path - Nunnally, who holds the key to the Damocles, and has been launching the F.L.E.I.J.As. She regains her sight, breaking Charles's Geass, and asks Lelouch if he would use his Geass on her to obtain the key. After being told that Damocles is to act as the symbol of the world's hatred, he proceeds to do so, taking the key from her and gaining absolute control over Damocles' destructive power.

Aftermath
With the Damocles in his hands, Lelouch declares himself the ruler of the world. In the following two months, the remnant Black Knights are rounded up, and repressions and pacifications of the conquered world begin. After the time skip, the Zero Requiem concludes with Lelouch's death at the hands of Suzaku (as Zero). The Damocles was then finally destroyed by sending it flying into the sun.