Zukaang

Zukaang is a Slash ship between Aang and Zuko in the Avatar: The Last Airbender series.

Canon
Aang and Zuko started off as enemies. The Fire Nation was at war with the rest of the world and Zuko was on a mission to find the avatar so that he could return home from his banishment. He attempted to capture Aang multiple times but always failed. Aang was eventually captured and imprisoned by Zhao so Zuko disguised him in order to rescue Aang so that he could capture him for himself. When Aang realized that it was Zuko who saved him, he chatted with him about his old Fire Nation friend, only for Zuko to attack him.

Zuko still attempted to capture Aang multiple times. Eventually, while Aang was in the spirit world, Zuko managed to capture his body and take him into a tundra cave to hide. While he was waiting in there, he complained about his sister who was a prodigy and compared Aang to him. Eventually, Katara arrived to save Aang and subdued Zuko. The group was about to leave Zuko to die in the harsh tundra conditions but Aang insisted on taking him so that he would not die.

Zuko eventually became a fugitive of the Fire Nation. However, he still wanted to capture Aang even though he would never be able to return to the Fire Nation. He eventually attempted to capture Appa but Iroh convinced him to release Appa instead. Zuko finally decided to try and move on until Azula offered to let him return home if he helped them fight Team Avatar and the Earth Kingdom. Zuko pondered the situation and eventually attacked Aang.

Zuko returned to the Fire Nation and was given credit for killing Aang but he remembered that Katara had spirit water and realized that Aang was still alive. Unsure what to do, Zuko hired an assassin to kill Aang. However, Zuko was still unhappy and eventually left the Fire Nation to go join Team Avatar and teach Aang firebending. Aang did not trust Zuko at first but eventually changed his mind. They worked together and hugged after the war ended.

Following the end of the war, Zuko became the Fire Lord and asked Aang to kill him if he ever became a tyrant. Aang reluctantly agreed to this and made a promise. Zuko later backed out of segregating the colonies once he realized that he was separating families. Roku tried to convince Aang to keep his promise and kill Zuko while finally revealing that he was Zuko's great-grandfather. Aang had a dream that he killed Zuko but eventually sorted out the issue without violence. They later discussed the issue and Zuko admitted that he should have not asked Aang to promise to kill him.

Fanon
Zukaang is a popular ship among the Avatar fandom and is one of the most popular slash ships. It especially became popular once Zuko joined Team Avatar. A lot fans were amused by the fact that Aang hugged Zuko from behind when begging for some of his fire. Some also saw the rainbow flames surrounding the both of them as an obvious sign. Many fans celebrated at the end of the series when the two hugged. Zukaang commonly rivals the Kataang, Maiko and Zutara ships.

Trivia

 * Aang is the reincarnation of Zuko's maternal great-grandfather Roku, making them spiritually related.