Kairi was originally a resident of Radiant Garden as one of the seven "Princesses of Heart". She has an encounter with Aqua in Birth by Sleep and is given a protective charm to keep her safe from darkness, which leads to her being sent to Destiny Islands when Xehanort performs an experiment where all six apprentices of Ansem the Wise forcefully rip out their hearts and caused the invasion of darkness; in addition, she inadvertently gains the power to wield the Keyblade after touching Aqua's Keyblade. At the beginning of the main series, she is fourteen years old. When Destiny Island is destroyed by Heartless, Kairi's heart is separated from her body and enters Sora's body. Kairi's body is in a deep sleep and can not wake up if she doesn't get her heart back. Her identity as a Princess of Heart is revealed along with the location of her heart. Learning of this, Sora gives up his heart in order to release hers and restore her heart back into her body. Soon after, Kairi finds Sora's Heartless and restores him back to human form. Kairi later gives Sora her lucky charm, which Sora promises to return. After Sora seals the door to Kingdom Hearts, Kairi is separated from him and left behind on the reforming Destiny Islands where she awaits his return.
During Chain of Memories, Naminé's memory-altering powers break the memories in Sora's heart as well as those of his friends on Destiny Islands, leading Kairi to lose her memories of him. In Kingdom Hearts II, Kairi and all of Sora's friends gradually remembers Sora as his own memories are restored. Kairi sends a letter she wrote out to sea in hopes that it will find its way to him. Later, Kairi is kidnapped by Axel, who hopes to use Kairi to lure Sora to him. However, Saïx takes Kairi from Axel and imprisons her and Pluto in a jail cell in the World That Never Was. She escapes her cell with the help of Naminé and they are saved from Saïx by Riku, in the guise of Xehanort's Heartless. Riku gives her the Keyblade Destiny's Embrace (デスティニープレイス?, lit. "Destiny Place") which she uses to fight off the Heartless that Saïx summons. Kairi reunites with Sora, and along with Donald, Goofy and King Mickey, the group face and defeat Xemnas. Kairi then returns with Sora and Riku to Destiny Islands where they receive a letter from King Mickey. As soon as Sora resolves to go on another journey, Kairi loans her lucky charm to him again.
Role in the SeriesIn the Spongebob series, Kairi ends up becoming a valued target for various dark rituals of the Villain League, most notably, restoring Lord Cobra, and freeing the Darkspawn. The young Princess of Heart was found and rescued by the Shell Lodge Squad during the events of SpongeBob and Friends Join The Rescuers, dedicating themselves to protecting her, even forming a strong bond with her as a kind of family. She currently stays in the Dragon Guardian's Temple under the care of Ignitus and the High Council. Kairi was introduced into the series by Tman, despite Scroopfan not wanting her in it from the beginning. In SpongeBob and Friends Meet Brother Bear, Kairi discovers through visions that Lord Shen, before the events of Kung Fu Panda 2, found peace with her when she was young because he was a close friend of her mother, but was separated from her by Cobra, and she reunites with Lord Shen in the adventure, where he becomes the general for the Shell Lodgers, and becomes her main caretaker. She also discovers that she has more to her past throughout multiple other adventures, such as her brotherly connection to Spyro, and inherited her caring heart from an ancient hero known as Tyro. She also gets her Kingdom Hearts III appearance early, along with Sora and Riku, after a time dilation caused by the events of Viral Vi-tor Gets Real. In Kingdom Hearts III, her physical death has become an alternate timeline while the SAFA Kingdom Hearts III becomes the focus of Princess Salvation, where Xehanort, revealed to be a darker replica created by Cobra and Architect, decides to step up his game and successfully captures Kairi, but doesn't use it for the Well of Souls, betraying the Villain League and plans to awaken The Great Cycle, where all worlds are consumed by Kingdom Hearts at once, using Kairi as leverage. In the end, the captured Princesses of Heart are finally freed, and she and Sora get married as she, Riku, King Mickey, Donald, Goofy, and all their KH friends take an eloping trip to Radiant Garden.
PTE Redux Coniditons
Kairi will pretty much play the same role in PTE as she does in SAF. However, she and Spyro will not have the same brother-sister relationship.