Avatar: The Last Airbender: Double Trouble
What if Aang had a twin? And what if she had secretly also been an Avatar? Well, that's exactly who Ling is. The twin sister to Aang who has hidden her Avatar abilities from the monks ever since she sent a rock flying at Aang's head when they were little. There had never been two Avatar's at once and she knows nothing good will come from telling. When her brother wakes her in the night, distraught, she doesn't question him when he says he wants to go for a ride, even though there's clearly a storm coming. Now they're a hundred years in the future, there's a war they have to stop and Ling doesn't know if she can keep her secret and help Aang save as many lives as possible.
