WHAT.....Kitara, who is the guy and so Sokka's dead and wait how does this dude know Kitara.....? confusion write another and explain
...I apologize for making it less than clear. This story takes place several hundred years after what we're watching. The character is one of the future Avatars, and he remembers Katara because she was so close to Aang--just like Aang remembered Avatar Roku. There is no set up or anything--the story is meant to stand alone.
(And it is spelled Katara, just so you know.)