Warning: Spoilers for the first two seasons of “Code Geass: Lelouch of the Rebellion” below.
Many newcomers to the franchise start with the two original anime series, which tells the story of Lelouch vi Britannia, the heir to the empire who’s sent to live in Japan. There, he receives the magical “Geass” ability, or the “Power of Kings,” which allows him to command anyone to do his bidding.
“Code Geass: Lelouch of the Rebellion,” or R1, aired in Japan from 2006 to 2007. Spanning 25 episodes, it details Lelouch’s Black Rebellion, in which he leads the Black Knights against the Empire of Britannia. For the essential “Code Geass” experience, many move on to the follow-up season, “Code Geass: Lelouch of the Rebellion R2.” The follow-up series was broadcast in 2008, with another 25 episodes. After Lelouch’s rebellion ends in failure, R2 begins when he’s captured and brainwashed by the forces of Britannia.
There are also two feature-length recaps of these two series that were released in 2008 and 2009 but are currently out of print, via My Media Chops.