The ending of the Shikimori manga is quite satisfying. The main characters reach a conclusion that feels right for their journey, and loose ends are neatly tied up.
He would be super excited. Zuko would probably be right there on the floor with Izumi, coaxing her to take those first steps. He might hold out a small, shiny object from the Fire Nation as an incentive.
One common theme could be their relationship exploration. Since they are the main characters, many fanfictions might delve into how they get closer and understand each other on a deeper level.
One common theme is the exploration of human nature. His characters often face internal conflicts that reflect different aspects of human nature, such as vanity in 'The Nose'.