Avatar: Seven Havens

The show is 26 episodes (divided into 2 "books") and premieres October 9:

"Seven Havens centers around a young Earthbender who discovers she’s the new Avatar after Korra in a world shattered by a devastating cataclysm. In this dangerous era, that title marks her as humanity’s destroyer, not its savior. Hunted by both human and spirit enemies, she and her long-lost twin must uncover their mysterious origins and save the Seven Havens before civilization’s last strongholds collapse.”