Ender's Game is a book series written by Orson Scott Card about a small boy called Ender. Ender is thought by the adults to be a terrifically smart strategist, so they take him to the Battle School (a school in space) so that he can become even better and lead them in the Third War against the Cockroaches from Outer Space.
Ender's Game Manga
Original Ender's Game manga
In the early issues of the Ender's Game manga, the premise was somewhat different. Rather than being an expert Battle Room player, Ender was a passable player of every concievable game, capable of winning even the You Lose Game. With his friends Bean and Alai, he wanders around North Carolina, using his skills to thwart miscellaneous villains.
In 1951, the focus of the series shifted, as Ender left home for the country of Command School. This marked the beginning of a series of long running plots, starting with the Bugger Sega, in which Ender goes to challenge the Bugger Queen, inventor of Battle Room, in her own territory. After this came the Piggy Saga, in which Ender, his girlfriend Novinha, and his pet canary Jane travel to the planet Lithium and try to prevent it from being destroyed by a diminuitive doctor.
The Shadow series
In 1977, a spinoff series entitled Shadow was launched, beginning with the Hegémon Saga. This series focused on Ender's brother, Peter Wiggin, who dreamed of being the world's greatest Hegémon master, and to accomplish this he travelled with Bean and his wife Petra around the world, capturing and training countries and using them in Hegémon battles.
The Ender's Game anime is a mostly-faithful adaption of the events of the original manga, beginning with the Bugger Saga. Although the previous stories are vital to understanding what is going on, nobody really misses them. The fans are mostly grateful for the addition of events established by the Shadow series.
The Engrish version of the anime is hated by many fans because Bean's name was changed to Julian, and his lover Nikolai was made his brother instead. =