Zuko had no one to turn to with Aang busy doing Avatar business and Toph always by his side to help him ,and Sokka and Suki figuring out wedding arrangements that left Zuko with one other choice, he had to ask Katara for help. Now Katara wasn't his first choice seeing that he had never really lost his feelings for her when he started getting involved with Mai. He did not want to ask Mai on the mission fearing she would get hurt and she was the"Lady". Only Fire Nation citizens could be Lord/Lady, it was Fire Nation code and also something the rest of the world abided by. During this mission Zuko and Katara fall in love, but will Fire Nation code destroy chances of them being together? And what will Mai have to say? (Let's pretend his uncle didn't die).