Kiyi was born to Ikem and Ursa, who went through life as Noren and Noriko respectively after having their faces changed by the Mother of Faces.
Meeting Team Avatar
When Noren invited Team Avatar into his family's house in 102 AG, Kiyi decided to talk to Zuko and Azula, who were, unbeknownst to either of them, actually her half-siblings. She asked them if they wanted to see her doll, a suggestion Azula bluntly refused and Zuko happily accepted. Kiyi told him that the toy was also named Kiyi as she thought it was "such a good name". When Zuko commented on the doll's haircut, Kiyi told him that she had tried to make the doll prettier, but accidentally cut too much of its hair off. Zuko responded that Azula used to do things like that to her own dolls as a little girl, prompting Azula to clarify that she cut off their heads, rather than their hair. After she was asked whether she wanted to see a demonstration, Kiyi refused and went behind Zuko in fear while hugging her doll tightly to herself. Shortly thereafter, Kiyi explained to her father that she was trying to be hospitable to their guests after he entered with Sokka. When Team Avatar left her family's house, Kiyi ran up to Zuko and begged him to come back some time again.
Kiyi met Zuko again when he returned some time after, giving him a hug and pulling him to have dinner with her and her family. After Zuko claimed her mother to be his own mother, Ursa, Kiyi grew confused and hugged her, though was passed to her father when they heard sounds coming from the roof. Before she could make sense of the situation, Azula barged into the family's home, causing Kiyi to scream for her mother. She was subsequently taken to safety by her father and Sokka as the princess fought with Zuko. Later, Kiyi and her father sat at a campfire, preparing a meal while her mother, who had regained her old face and memories, began talking about her past with Zuko.
Visiting the Fire Nation Capital
Some time later, Kiyi boarded the ship that would take her, her family, Zuko, and Team Avatar to the Fire Nation Capital for the first time since Ursa's exile. During the journey, she entertained herself by riding on the back of a flying dolphin fish along with Aang until Ursa realized the possible danger of riding a wild animal and called them back. As Aang brought her back on to the boat, she was pulled into a tight hug by her mother, who stated that she could not lose her. However, not recognizing Ursa as her mother due to the restoration of her old face, Kiyi screamed to be released. She ran to hug her father's leg and urged him to accompany her downstairs, which prompted Ikem to pick her up and take her below the deck.
After having been made aware of a possible security threat, Zuko diverted course and arranged for his cruiser to rendezvous with a submarine, much to Kiyi's surprise. She met Iroh and Suki shortly thereafter, remarking to her brother that the Kyoshi Warrior was pretty. As she prepared to cross the plank to the submarine, Zuko suggested for her to accompany her mother as she might be scared. After initially refusing her half-brother's request, Kiyi relented and agreed to take her mother's hand as a favor to Zuko.
Kiyi and her family were transferred to a carriage after reaching the mainland and set course to the capital through a hidden route, where the caravan was promptly ambushed by the New Ozai Society. Though Ursa urged Kiyi to remain brave, Kiyi insisted that she was not scared and recoiled from her mother's touch, complaining that her hands were too cold. After a brief altercation, Ukano and his organization were able to subdue Zuko and the Kyoshi Warriors, and prepared to burn the carriage in which Kiyi and her family were taking refuge. The fight resumed after Kei Lo freed Zuko and reinforcements arrived via hot air balloon, exciting Kiyi despite all the danger.
Later, after the attackers were subdued, Kiyi and her family finally arrived at the Fire Nation Royal Palace. Kiyi eagerly dragged her father along to explore the palace, despite Ikem's concern that she should rest after an exciting afternoon. Kiyi brushed him off, saying that "Zuzu" would keep them safe, which surprised both Zuko and Ursa who could not fathom why she used that nickname. Zuko remarked that it sounded much nicer coming from Kiyi than Azula.