Nothing's Like Before

Based on the theory that the Princesses of Heart have to be immortal or reincarnated, if they've been holding up what's left of the Light since the Keyblade War. Before an earlier Kairi's life comes to an end, she's able to meet the infant Sora on Destiny Islands. And even then, their hearts are connected and their souls bound. Finding hope there, Kairi's able to pass on in peace.