"I may be an earthbender, but through my father's bloodline I am a Fire Nation citizen! My father taught me to always be loyal to the Fire Nation, to my people."
— Kori explaining to Zuko her resistance against the Harmony Restoration Movement.
Kori Morishita was the daughter of Morishita, the mayor of Yu Dao, and his wife. She was shown to be protective of her home and went so far as to attempt an assassination of Fire LordZuko in order to preserve her home. Her mother was an earthbender and she too inherited the ability.
Kori was born to Mayor Morishita and his wife in the Fire Nationcolony of Yu Dao, and was raised to honor both the Fire Nation Royal Family and her hometown. During her youth, she was given some form of earthbending training as well as additional weapons training, where she learned to use a meteor hammer. In early 100 ASC, she met Sneers, a former Earth Kingdom rebel who had traveled to Yu Dao after the dissolution of his group, and the two of them fell in love and began a romantic relationship.
While Kori succeeded in incapacitating the guards, Zuko proved to be too much for her and she was captured. Zuko began interrogating her and brought her back to Yu Dao where he met her father, Mayor Morishita, and her earthbender mother. Initially, Zuko attempted to persuade Kori and her family to return to the Fire Nation; however, Kori, her parents, and a closer look at the life of Yu Dao convinced Zuko that the Fire Nation colonies should stay.
Zuko's decision to withdraw his support for the Harmony Restoration Movement, however, made the tensions rise outside the gates of Yu Dao, and Kori organized her cousins, both earthbenders and firebenders, to train for battle.
Some time after the Freedom Fighters' arrival in Yu Dao, Kori and Sneers' romance became strained after Kori learned that Sneers had become one of the leading protesters outside the gates of Yu Dao. When Sneers said that it was time Kori choose a side, the Earth Kingdom or the Fire Nation, she stated that she had already chosen, namely to be an earthbending Fire Nation citizen who lived in Yu Dao. As she walked away from Sneers, she left him with an ultimatum: fight for her colony's right to stay in the Earth Kingdom, or side with Smellerbee and break off their relationship.
Kori continued her relationship with Sneers after he chose to side with the Yu Dao Resistance. When Aang and Katara returned to Yu Dao to urge the colonials to evacuate, Kori, together with other members of the Resistance, attacked them with an assortment of weapons, assuming that they had arrived to force them from their homes. Aang proceeded to inform them of the true reason for their arrival, but Kori was undeterred, and boasted that they could handle the Freedom Fighters. However, when Aang revealed that the Earth King and his army were marching toward Yu Dao, she attempted to persuade Aang to help them fight the Earth King, albeit unsuccessfully. As a last resort, Kori introduced the Avatar to the Yu Dao Chapter of the Official Avatar Aang Fan Club.
When the Freedom Fighters breached the wall with a drilling machine, Sneers reluctantly introduced Kori to Smellerbee. Attempts to reason with the Freedom Fighters ended in failure, as a skirmish ensued between the Yu Dao Resistance and the Freedom Fighters. At the same time, the armies of both the Earth Kingdom and Fire Nation arrived and started to battle. GeneralHow entered the town gates and demanded the colonials surrender. Kori refused to cooperate and threw her meteor hammer at him, only for her opponent to shatter it. The battle ended when Aang entered the Avatar State, used earthbending to uplift Yu Dao from the battle, saved Fire Lord Zuko, and managed to reason with the Earth King to spare Yu Dao.
After the solution of the escalating crisis and an agreement between Zuko and Earth King Kuei, Kori attended a meeting in the governor's place of Yu Dao, together with Sneers, her family, Avatar Aang, Zuko, and other dignitaries to discuss the future of the city.
Kori was shown to be headstrong and "rash", according to her father. While usually tame, Kori was fiercely defensive of her homeland of Yu Dao, going as far as to attempt an assassination on the Fire Lord to protect the interests of her home.
Kori, being of mixed heritage, developed her earthbending abilities since she was a child. She combined her bending skills with her meteor hammer. By using a weapon made of rock, she was able to use her bending to control the directions of the attack, thus making her a greater threat.