Maiko

Maiko is a Het ship between Zuko and Mai in the Avatar: The Last Airbender series.

Canon
Zuko and Mai knew each other since they were children. Mai developed a crush on Zuko and Azula and Ty Lee noticed this. Azula decided that it would be funny to create an awkward moment between them and convinced her mother to let Zuko play with them. Azula placed an apple on top of Mai's head and lit it on fire. Zuko immediately tackled her into the fountain in order to save her. Azula and Ty Lee laughed at them and remarked that they looked cute together. Mai was embarrassed while Zuko was simply annoyed that he got wet.

Zuko was banished for a while but was eventually allowed to return home after he helped Azula defeat Aang. He and Mai began dating while they were still in Ba Sing Se. They kissed there while they were on a date and again while they were on a ship that was returning home. Zuko complained about his uncertainty in life but Mai simply stated that she only asked if he was cold. The two later went on a romantic picnic until Azula came to interrupt them.

Zuko and Mai would later take a vacation to Ember Island along with Azula and Ty Lee. Mai was fitting in well while Zuko was not since Azula had decided that they should hide heir royal status. They were later invited to a party and the strain between Zuko and Mai began to show. Zuko was irritated when another man was flirted with Mai. This led to a screaming argument and Zuko called Mai a "blah" which caused her to break up with him. However, after Zuko revealed that he was mad at himself at a bonfire on the beach, they got back together.

Zuko and Mai continued their relationship for a while until Zuko decided to leave the Fire Nation and train Aang. He broke up with Mai over a letter in order to protect her. However, she would later confront him over this at the Boiling Rock. The warden attempted to have the line cut on the gondola while Zuko was escaping so Mai saved him and explained to Zuko that she loved Zuko more than she feared Azula. At Zuko's coronation as Fire Lord, he was having trouble with getting dressed due to his injuries so Mai arrived to help him put his robe on. They got back together but Mai warned Zuko not to break up with her again.

Over a year later, Zuko was having trouble with sleeping as there was a crisis in Yu Dao. He also visited his father Ozai in prison without telling anybody. Mai eventually found out and asked Zuko why he kept secrets from her. She then decided that Zuko loved secrets more than he loved her and broke up with him yet again.

Zuko left for a while to find his mother and returned after doing so. Mai was dating Kei Lo by then who warned her of an assassination attempt on the Fire Lord. She helped with a mission to protect him. Zuko was happy to see Mai and learned about her dating Kei Lo. Later, Mai's brother Tom-Tom was captured by the Kemurikage. Zuko told her that he would get her brother back and called Avatar Aang for help.

Fanon
Maiko is a very popular ship in the Avatar fandom. Many fans ship it as an endgame ship since they were together at the end of the series. When the Legend of Korra was announced and it was revealed that Aang and Katara got married, fans assumed that the same thing would soon happen with Zuko and Mai. However, nothing between them was ever revealed and they broke up again in the first comic trilogy. While Zuko was revealed to have a daughter, the mother is still unknown. Some fans hope that Mai is the mother and that they will get back together in the upcoming comic trilogy. Maiko is usually shipped along with Kataang and commonly rivals the Zutara, Jinko, Soko and Toko ships.