Kairi

Kairi is one of the three main characters who appears in all three Kingdom Hearts games. She is the love interest of Sora and Riku, who compete for her in the first part of the series.

Kingdom Hearts
In the original game, Kairi is attacked by Heartless, which leaves her as an empty shell. When Sora and Riku are taken from the island, they are seperated from Kairi, and each other. Riku later finds Kairi, and uses the power of darkness to restore her (which eventually leads to Riku being possessed by Ansem). Sora also tries to find her, to no avail, until he (along with Donald and Goofy) is captured by a pirate ship. On the ship, he finds Riku, who is taking care of Kairi, and trying to heal her. Riku takes her to Hollow Bastion, and it is revealed that she is one of the Princesses of Heart. Sora and Riku fight, and Sora wins, leaving him control of Kairi's empty body. By using Riku's Keyblade, and by sacrificing his own heart, Sora brings Kairi back to life, and Sora is turned into a Heartless. Kairi, Donald, and Goofy later find Sora in his Heartless form. Although Donald and Goofy begin to attack him, Kairi realizes that the Shadow is indeed Sora, and by showing him her love for him (by protecting him from other Heartless), Sora is changed back to his human self. In the conclusion of the game, Kairi and Sora are seen after Sora locks Kingdom Hearts. Kairi is sent back to the Destiny Islands, while Sora is transported to a different world.

Kingdom Hearts II
Kairi (now older than she was in the first game) lives her life normally in Destiny Island. She misses Sora, but because he was inside of the flower pod,which he was in to restore his memory, she could not remember his name. After the conclusion of Roxas's story, she remembers his name to be Sora. One day, Axel comes to the Destiny Islands and tells Kairi to come with him. She refuses until Axel summons a group of Nobodies. She goes with him, and eventually meets Namine and Riku, whose appearance has changed to that of Ansem's. Riku leads her to Sora and is attacked by a group of Heartless. He hands Kairi a Keyblade, and Kairi successfully fends off the remaining Heartless. She is then reunited with Sora. After Sora and Riku lock Kingdom Hearts, she is sent back to the Destiny Islands, but is once again separated from her friends. After they defeat the final boss, they also return to the Islands, and the game ends.