Who is kairi

Kairi is a close friend of Sora and Riku, she gets lost in the first game by the darkness, as Riku captures her and keeps her away from Sora, but at the end of the first KH game, Sora saves her and Riku, Riku goes into the Door To Darkness with Mickey while Kairi goes back to her home, Destiny Island. In the second game she meets Sora again at about close to the end of the game