Code Geass R2 E.21

Within the Sword of Akasha, Lelouch learns the truth of his mother's death from the Emperor and Marianne herself. They reveal Ragnarök will merge everyone into the collective unconscious. However, Lelouch disagrees with their reasoning, believing there is no future in that life, and uses his Geass on the collective unconscious to stop Ragnarök, resulting in his parents' deaths. One month later, Lelouch forcefully inaugurates himself as the new Emperor of Britannia with Suzaku now at his side.