The story begins at Zuko's family beach house where Katara, Sokka, Suki and Toph watch Aaang practice his firebending with Zuko coaching him. After practice is done the Gaang head out to the private beach for some fun in the sun but this is soon interrupted when a female clad head to toe in black suddenly appears and attacks Aaang at first they think it is Azula but this is soon shown to be false when their attacker uses waterbending against them but although she is a powerful bender and attacks them with a sure ferocity they are able with team work to capture her. Then they get the shock of their lives when they unmask her and she is revealed to be Katara but this one has no hair on her head and her eyes have none of the hope and kindness the other Katara has in hers. They ask her who she is and why does she look like Katara. The Dark Katara explains she is from an alternate timeline four years in the future in her timeline Aaang ran away instead of facing the Fire Lord leading to a Fire Nation victory and she watched as her family and friends were killed and she spent two years in a Fire Nation prison being tortured day and night by Azula and used as a personal play toy by any of the guards who wanted to use her for their pleasure. She also explains her lack of hair Azula burned it off and it never grew back. Katara was all ready to die when she was saved by her timelines Zuko who broke her out of prison and for two years the two have traveled together leading a band of guerrilla fighters. The Gaang listen to her story in shock and then ask her why did she attack Aaang, Dark Katara laughs and explains that there are three people she wants to kill with her own hands Fire Lord Ozai, Azula and most of all Aaang she hates him with all her heart she hates him. All feelings of love and friendship she may have had for him were tortured out of her. The Gaang walk away from her to discuss what they should do with her knowing they can't keep her prisoner forever and they can't kill her (and also remember at this point Aaang hasn't learned energy bending yet so he can't take her bending away). Finally they decide they will let her go but only if she promises to behave and not to kill Aaang Dark Katara thinks it over and agrees to their demands for the meantime but she demands that she only wants to be around Zuko explaining that being around Sokka, Toph, and Suki bring up to many painful memories for her and that her hatred of Aaang would make being around him impossible for her so that leaves Zuko. Once she is let go she and Zuko go inside the house once there Dark Katara ask if it is all right if she takes a bath Zuko says yes and then she proceeds to take off her top right in front of him showing a body marred with burn scars but still attractive this of course causes Zuko much embarrassment and he looks away but Dark Katara just laughs and tells him that her Zuko has seen her nude plenty of times Zuko ask how close she and his counterpart had gotten during their two years fighting against Ozai Dark Katara laughs and simply says they have gotten very close. Zuko then feels her hand on his shoulder she spins him around and kisses him.
That is all I have so if any of you out there think you can do anything with what I have written you are than welcome to do something with it and make any changes you wish to the story and characters.