Unlike her successors, Roku and Aang, Kyoshi was determined that only true justice could bring peace, and had no qualms about killing enemies to achieve this goal. Employing these methods, she was a generally effective Avatar. However, some of her actions also caused long-term problems for the Earth Kingdom; while ushering the world into a 233 year-long era of peace, the death of Chin the Conqueror and her foundation of the Dai Li would lead to the decline, corruption, and fall of her home country. Because of this, Kyoshi later came to deeply regret the creation of the Dai Li.
Kyoshi was born in the year 312 BG on a peninsula off the tip of the southwestern Earth Kingdom that would one day become Kyoshi Island. She, like all Avatars, mastered all four elements and the Avatar State. When Kyoshi visited the ports of her homeland, she constantly had to put carousing men in their place after they caused trouble to the female villagers. Eventually, she decided to train the women in defensive combat so that they could defend themselves. These women later formed the first band of Kyoshi Warriors.
Stopping Chin the Conqueror
During Kyoshi's life, the 46th Earth King's rule was unpopular among the populace of the Earth Kingdom. Using this to his advantage, a warlord named Chin launched a war to conquer the continent. He was successful until he reached the peninsula where Kyoshi lived. When he refused to listen to Kyoshi, she confronted him and separated the peninsula from the mainland through a combination of all four bending arts, save for waterbending, and the Avatar State, forming Kyoshi Island and thereby protecting her homeland from subsequent threats. An indignant Chin was left standing on the edge of a cliff, which began to crumble beneath his feet, causing him to fall into the sea, where he subsequently drowned. His death ushered the world into a great era of peace.
Because of Kyoshi's act, the people of Chin Village on the mainland founded Avatar Day to vilify Kyoshi, and all succeeding Avatars, for the death of their leader. The people of Kyoshi Island, meanwhile, founded "Kyoshi Day" on the same day as Avatar Day, to honor her creation of the island and the restoration of peace to their village. They also erected a large totem, topped with a statue of Kyoshi in her memory.
History with the 46th Earth King
Sometime after her final confrontation with Chin, Kyoshi was summoned to Ba Sing Se upon the request of the Earth King, since his unpopular rule had led to a peasant uprising in the city. By the time Kyoshi reached the city, the peasants had already destroyed everything that represented the "old government", including ancient and valuable artifacts that held historical and cultural importance. The King demanded that she stop the uprising by whatever means necessary. However, Kyoshi staunchly refused, stating that it would not be right for her to do so. Incensed by her defiance, the Earth King ordered her arrest, but a display of the Avatar's power and a warning intimidated him into a compromise. The Earth King agreed to give the peasants a voice in his ruling, while Kyoshi in turn agreed to protect Ba Sing Se's cultural heritage from further desecration. She proceeded to train an elite platoon of earthbenders, though their subsequent corruption weighed heavily on Kyoshi in her afterlife.
Kyoshi died in the year 82 BG at the age of 230, making her the oldest Avatar and human in history. Her daughter Koko succeeded her as the leader of Kyoshi Island, and she reincarnated as Fire Nation native Roku.
Appearances throughout Aang's life
During his trip to Kyoshi Island, Aang observed the statue erected in her honor. She thereafter appeared in a vision as the most recent Earth Kingdom Avatar when Avatar Roku was explaining the nature of the Avatar State to Aang. Kyoshi later manifested herself through Aang, as Roku had done on the winter solstice, to testify in a trial proving the Avatar's innocence, though she confessed to killing Chin while doing so.
Before the arrival of Sozin's Comet, Aang summoned Kyoshi's spirit, seeking advice on how to defeat Phoenix KingOzai without killing him. Kyoshi reminded him that her forceful ending of Chin the Conqueror's war for dominance brought a great era of peace. Aang pointed out that she was not directly responsible for Chin's death, arguing that it was a result of his own arrogance. Kyoshi said she saw no difference in this, and told him that she would have done anything to stop Chin. She left Aang, telling him that only justice would bring peace. Aang regretted consulting Kyoshi on this complex matter after hearing her advice.
Appearance in Korra's life
Kyoshi, alongside many other past Avatars, appeared to Korra after she had lost her bending to Amon. This appearance was representative of Korra's ability to establish a connection with her spiritual side and for the purpose of having her bending restored.
After Korra had lost her memory, Kyoshi appeared before her, taking over from Avatar Roku, and informed the young Avatar that if she did not reconnect with her Avatar Spirit, darkness would engulf the world and she would die, ending the era of the Avatar.
While Unalaq was attacking Raava, Korra envisioned Kyoshi as part of the Avatar lineup, which she had seen prior to regaining her bending; however, the latter's connection to Korra was severed due to Unalaq's assault on and subsequent destruction of the light spirit.
As the Avatar, Kyoshi was able to bend all four elements and enter the Avatar State at will. Her most spectacular known feat was using the Avatar State to separate her home peninsula from the Earth Kingdom mainland, and push it far out to sea to create Kyoshi Island. To do so, she first cut down to the earth's mantle with earth and lavabending to sever the landmasses, followed by airbending to push the island out to sea. This is one of the two known instances in which Kyoshi used the noncontinuous Avatar State, the other being when she levitated two massive badgermole statues.
On the golden button on the right arm guard of the Kyoshi Warriors, and on the fan that the statue of Avatar Kyoshi held to her face, is the word 京. The other fan, the one on her outstretched arm, is the word 士. In Japanese, 京士 is pronounced 'kyōshi' and translated as 'capital samurai.' However, on the mural in her shrine, her name appeared as 虛子 (Kyoshi in Japanese, a near-homophone with 京士, but with a shorter 'o' sound). Kyoshi (虛子) is a proper name in Japanese as, for example, the poet Takahama Kyoshi (高浜 虚子).
In the episode "The Southern Air Temple", Kyoshi was seen to the right on the painting in the Earth Kingdom's Avatar Temple. However, the statue that preceded Roku's statue in the Southern Air Temple is not Kyoshi's.
In a concept piece for the episode, however, an early depiction of Kyoshi does stand after Kuruk.
Kyoshi also had the largest feet of any Avatar, and was the largest known Avatar in terms of physicality; when seen confronting Chin the Conqueror in "Avatar Day", and the time she faced the 46th Earth King's guards, she clearly appears several heads taller than them.
In a chibi comic, Kyoshi was portrayed as a gym teacher. This can be a reference to the meaning of her name, 'teacher', and the fact that she began two different factions of warriors, training them in two different fighting styles.
Kyoshi is the first known Avatar to have had descendants.
Avatar Kyoshi's legacy and work as Avatar has started two groups: the Kyoshi Warriors and the Dai Li, both of which Azula made use of to conquer Ba Sing Se.
Kyoshi, Roku, Aang, and Korra are all known to have defied the leader(s) of their respective nations: Kyoshi, at first, refused to aid the 46th Earth King when he asked her to intervene in the Peasant Uprising in Ba Sing Se; Roku nearly killed Fire LordSozin in an attempt to put a stop to his imperialistic actions; Aang did not move to the Eastern Air Temple when he was told to and instead ran away; and Korra started a civil war against ChiefUnalaq.
Kyoshi has never been seen without her signature makeup.