Code Geass: Nightmare of Nunnally

In the year 2010, the Holy Empire of Brittania declared war on Japan. Powerless to stop them, Japan surrendered in less than a month. Freedom was lost and Japan was renamed "Area 11" and its people became known as "Elevens." Lelouch is a Brittanian and his friend Suzaku, born an eleven, has achieved the status of honorary Brittanian. As a boy Lelouch vowed to crush his own government, but now seven years later and in high school, he's accepted that he can't change anything. That is until he meets a mysterious girl that gives him the power to control people's minds - the power of Geass! He dons a mask and becomes the ruthless terrorist known only as Zero, destroying any who might stand in his path - including his boyhood friend Suzaku!
(Source: Bandai Entertainment)

The Empire of Brittania has invaded Japan using giant robot weapons called Knightmare Frames. Japan is now referred to as Area 11, and its people the 11s. A Brittanian who was living in Japan at the time, Lelouch, vowed to his Japanese friend Suzaku that he'd destroy Brittania. Years later, Lelouch is in high school, but regularly skips out of school to go play chess and gamble on himself.
One day, he stumbles on terrorists 11s who've stolen a military secret and is caught by a member of the Brittanian task force sent after them, who is Suzaku. As the rest of the squad arrives, Suzaku is shot for disobeying orders, while the military secret, a young girl, gives Lelouch the power to make anyone obey any order. He takes command of the terrorists and leads them to crush the approaching Brittanian force. However, Suzaku is secretly made the pilot of Brittania's brand new test model Knightmare, Lancelot. Lelouch becomes the masked king Zero to lead the rebellion to defeat Brittania.

The Empire of Brittania has invaded Japan using giant robot weapons called Knightmare Frames. Japan is now referred to as Area 11, and its people the 11s. A Brittanian who was living in Japan at the time, Lelouch, vowed to his Japanese friend Suzaku that he'd destroy Brittania. Years later, Lelouch is in high school, but regularly skips out of school to go play chess and gamble on himself.  One day, he stumbles on terrorists 11s who've stolen a military secret and is caught by a member of the Brittanian task force sent after them, who is Suzaku. As the rest of the squad arrives, Suzaku is shot for disobeying orders, while the military secret, a young girl, gives Lelouch the power to make anyone obey any order. He takes command of the terrorists and leads them to crush the approaching Brittanian force. However, Suzaku is secretly made the pilot of Brittania's brand new test model Knightmare, Lancelot. Lelouch becomes the masked king Zero to lead the rebellion to defeat Brittania.
This series follows Suzaku's side of the story, while Lelouch of the Rebellion follow's Lelouch's.