A terrible alternate future
Surprised
Princess Azula and Prince Zuko returned to the Fire Nation in triumph. Even Ozai had to admit, his elder child had served his purpose. He would not be able to inherit the throne, but there would be a nice dukedom for him. Ozai did reward success and Zuko had succeeded.
As for Ozai's meddlesome brother, Iroh would have to be executed. A nice public one to kill off that sickly branch of the family. From Ozai and Azula would come a new race of Firebenders, stronger and better and more powerful than ever. In fact, the double execution of the Avatar and the Dragon of the West was a fine way to mark the former darkest day.
When the order for execution had been read, Ozai had been pleased to see no emotion in his son's eyes. Perhaps there was some mettle in the weakling after all. He had to say, he was definitely impressed by the sheer cold-bloodedness of Zuko betraying his beloved uncle. He never expected such ruthlessness. In fact, it pleased him.
Yet, fate was not so simple. The night of Iroh's execution, Zuko was found dead in his room, with a note asking the spirits to have mercy on his sinful soul. "I know I am condemned in this world and in every other life. I accept this fate."
Ozai was surprised at the poisoned corpse. He had thought his weak son had learned to be ruthless. He was wrong.
Ozai was even more surprised at the dagger in his ribs. He thought his ruthless daughter loved him. He was wrong.