Knights of the Round Uprising

Background
After stopping his parents plan to unleash Ragnarok across the world, Lelouch installed himself as the 99th Emperor of the Holy Britannian Empire, with Suzaku Kururugi as his personal knight; the Knight of Zero. However, some within the empire refused to recognize Lelouch as their new emperor and set out to usurp him from the throne.

The Battle
A group of the previous emperor's loyalists, led by the Knights of the Round were enroute to Pendragon, to remove Lelouch from power; as they approached, they were intercepted by Suzaku who was behind the controls, of the Lancelot Albion. Determined to protect Lelouch, Suzaku unleashed the Albion's power, killing the knights Dorthea Ernst and Monica Kruszewski, as well as destroying all of the Sutherlands; Gino suddenly attacks with the Tristan, while trying to convince Suzaku to leave the fight, to which Suzaku responds to him that he should be the one to leave. Suzaku disables the Tristan, but not before asking Gino whether he'd prefer to remain an ally of Britannia and Suzaku, or to rebel against it.

Bismarck in the Galahad soon steps in, Excalibur drawn; refusing to recognize Suzaku's title as the 'Knight of Zero'; he activates his Geass power, which allows him to see into the future fore a few seconds. With the knowledge that the Zero Requiem's fate was in the balance, Lelouch 'activated' Suzaku's Geass command to 'live'; with his ability now active, Suzaku was able to overcome Bismarck's Geass; slicing the Galahad and the Excalibur in half, Bismarck dies, stating his failure to empress Marianne.

Outcome
Now with his position as emperor secure, Lelouch soon announces to the world that the Holy Britannian Empire will join the United Federation of Nations; to the shock of those who were watching the battle.