Kira was a Gelfling, one of only two to survive the Gelfling genocide conducted by the Garthim. She lived because her mother stuffed Kira (a toddler at the time) into a knothole in a tree. Kira then watched as her mother was seized by a Garthim and killed.
Sometime later, the young Kira emerged from the tree and wandered through the forests alone and afraid, until she came upon a village of Podlings. They immediately recognized that Kira was a Gelfling and took her into their care and protection. She was adopted by the Podling woman Ydra, who raised her and taught her how to communicate with plants, animals, and "all the living things."
As she grew, Kira also found and adopted a strange, furry and violent creature that she named Fizzgig. Only she and the Podlings could interact with him; he would attack anyone else. Hearing Fizzgig barking at something, Kira found, to her surprise, another Gelfling, named Jen, trapped in a mudhole. She freed Jen by summoning a mud-dwelling nebrie who lifted him up out of the slime, and then the pair (with Fizzgig in tow) returned to her village.
Jen explained his quest- including the Great Conjunction -to Kira during a Podling festival, which was interrupted by a party of Gathim simultaneously searching for Jen and raiding the village for slaves. Several, including Ydra, were taken. After the Skeksis Chamberlain mysteriously stopped one of the Garthim from killing Jen, he and Kira fled into the woods, where they spent the night.
In the morning, the pair found the ruins of a Gelfling city where they were approached by the Chamberlain who attempted to get them to come with them. They refused and fled. Deciding to help Jen in his quest (as well as to rescue the captured Podlings), Kira got them to the Castle of the Crystal by riding on Landstriders. After a battle with some Garthim and a failed attempt to free the captive Podlings, the two Gelflings infiltrated the castle via the sewer.
Here they were captured by the Chamberlain, who buried Jen in a cave-in, and then brought Kira before the General. At the suggestion of the Scientist (and over the objection of the High Priest), Kira was taken to the Chamber of Life to have her essence drained. Here, Aughra urged her to call to the caged animals for help. Responding to her cries, the animals escaped, swarmed the Scientist, and knocked him down the castle shaft, freeing Kira.
Told more of the Great Conjunction by Aughra, Kira sneaked into the Crystal Chamber by following the Skeksis, at the same time as Jen (who had survived the cave-in). Her presence was given away by Fizzgig's eager barking. When Jen leaped onto the top of the Dark Crystal to escape a Garthim and dropped the Crystal shard, Kira retrieved it and threw it back to him...at the cost of her own life. While she was distracted returning the shard to Jen, Kira was stabbed to death by the High Priest.