Avatar the Last Airbender - Book 4: Air (The Master of the Lion Turtles)
21 parts Complete 5 years after the end of the 100 year war and the defeat of Lord Ozai, Fire Lord Zuko and Avatar Aang have succeeded in producing a plan for the new Republic City, that will become a safe haven for immigrants from all nations that have been displaced by the war. When Zuko receives reports of a group of four bandits stealing from the construction site he calls the Gaang back together to figure out their plan. However, Aang is distracted by one key point in the case: there appears to be an airbender on the team of bandits...is he no longer "The Last Airbender?"
Some Kataang fluff and angst...plus some slow burn Zukka ;)
Disclaimer: I do not own any of the original characters from ATLA