Kairi

One year after the events of Kingdom Hearts Birth by Sleep, Radiant Garden became shrouded by darkness and everyone was scattered across the universe. Kairi appears on the Destiny Islands during a meteor shower, appearing floating in the water on the beach; though it is believed that Ansem, Seeker of Darkness had sent Kairi to the islands as an experiment to test any possible connection between the Keyblade wielders and the Princesses of Heart, her arrival was actually due to the protective spell Aqua had cast on her one year earlier.^[1]Sora, then five years old as well, carefully approaches her and asks, "Who are you? Where did you come from?"

Sometime later, Sora and Riku were in the Secret Place and talking about "the new girl at the mayor's house". This provides the player a kind of insight into her origins: Kairi is not a native of the Destiny Islands, and is the adoptive daughter of their mayor.

“	So, suppose you get to another world. What would you do there?	”
—Kairi to Riku

Kairi later becomes very close friends with Sora and Riku who playfully compete for her attention. She often supports these competitions, although she does not know they were contests for her affection and not just innocent rivalry. She bears no memory of her life before the Islands, and her mysterious past sparks curiosity in Sora and Riku, who are anxious to leave Destiny Islands and see other worlds.

This leads the trio to build a raft in the hopes of traveling to other worlds. However, before they can leave, their islands are attacked by the Heartless, and Sora finds Kairi in their Secret Place. She turns towards him, looking sad and a little ill, and then a huge gust of wind sweeps through a door in the back of the cave and Kairi flies towards him. Sora opens his arms to catch her, but she vanishes right as she is about to be swept into his embrace.

During this time, it is speculated that Kairi's heart chose Sora as a vessel and when she passed through him, her heart was left behind in him while her body vanished to some distant world.

Sora and Kairi watch the sunset.

Added by Kai Maciel

She then becomes the game's driving force, as much of the game's story centers around Sora's and Riku's attempts at finding Kairi. However, Riku is hostile to Sora (having been manipulated by Maleficent into believing that Sora no longer cared for either Kairi or himself).

Throughout Sora's journey, he encounters multiple images of Kairi without knowing about Kairi's heart being a part of his. First, when he wakes up in a motel room after his fight with Leon, and sees Yuffie in Kairi's form and mistakes her to be Kairi until she tells him who she is. Later when he visits the Magician's Study behind the door of the Third District, Kairi appears to him and tells him how much the study reminds her of their Secret Place, but she disappears when Goofy calls to him.

When Sora crash lands into Deep Jungle, she reappears again for a short moment, right behind Tarzan, then disappears again. Finally, before setting off to Hollow Bastion, Goofy and Donald encourage Sora to believe in himself, then Kairi says from within "I believe in you." before pulling him into one of her lost memories about her grandmother telling her younger self a story about the light. These encounters speculate that Kairi was experiencing Sora's journey from within his heart, including befriending Donald and Goofy.

Riku finds her first, but she is in a comatose state, with a vacant, lifeless expression and a limp body. She'd lost her heart and because of her Princess status, her body remained untouched by the darkness that usually produced a Heartless. With empty promises by Maleficent, Riku was convinced that he alone could locate Kairi's heart and restore her to health. When inside Monstro, Riku attempts to kidnap Pinocchio in hopes to use his heart to restore Kairi's. This act confuses Sora as he hasn't learned of her fate. His attempt fails and he is forced to retreat.

In Neverland, Sora finally encounters her body, along with a painful reunion with Riku; who is very defensive about her and ends up locking her in a room with Wendy so that Sora can't get to her. When Sora reaches the room below her cell, he extends his hand towards her, desperately hoping for a reaction as he is just now discovering the full lengths of Kairi's condition.

Unconsciously, her hand twitches before going still again, much to Sora's relief. Riku then takes her away yet again, having new knowledge of where Kairi's heart might be. After the defeat of Captain Hook, Goofy ponders aloud whether or not Kairi had indeed lost her heart, but Donald, not wanting to upset Sora, promptly shushes him. Sora, however, appears to be in denial, pondering over his disbelief that he could fly and whether or not Kairi would believe him.

Their friendship severed for the time being, Sora continues his journey, destined to clash with Riku in the near future once again over Kairi.

Eventually, Sora follows Riku and Maleficent to the world of Hollow Bastion where he too learns of Kairi's fate. However, Ansem, Seeker of Darkness, while possessing Riku, reveals that Kairi's heart has been resting within Sora all along, which explains all the visions he has had of her during his journey. Furthermore, Kairi is one of thePrincesses of Heart, a maiden whose heart holds no darkness, and is needed to open the Final Keyhole. He then attempts to take her heart from Sora, but he defends himself to protect it.

After winning a fight and driving Ansem from Hollow Bastion, Sora sacrifices himself using the Keyblade of People's Hearts to free Kairi's heart, and is turned into a Shadow Heartless. Awakened as her heart is finally restored, Kairi runs towards him, but as soon as her fingers touch him, he vanishes. Refusing to believe that Sora is gone, Kairi prepares to fight the Shadow Heartless that surround her, along with Donald and Goofy.

“	This time, I'll protect you!	”
—Kairi to Sora's Heartless (whilst shielding him from the Heartless attack)

However, once Ansem reappears and Riku's spirit stops him from attacking Kairi, she flees. Devastated, she, along with Donald and Goofy, attempt to escape from Hollow Bastion. But just as they are cornered by the Heartless, she recognizes Sora's Heartless from the crowd and manages to bring Sora back from the darkness by embracing him and promising to protect him. The group escapes Hollow Bastion, revealed to be Kairi's home world, and find shelter in Traverse Town where she could be protected by Leon and the others.

Sora finds Kairi in the underground water tunnel after talking with Leon. She states absentmindedly how much this place reminds her of their Secret Place. While lost in darkness, Sora witnessed one of Kairi's memories of her as a little girl wandering around the Hollow Bastion library with her grandmother. Sora mentions this and it is revealed that after her heart was restored, Kairi could remember certain things from her past. Though Kairi wants to help rescue Riku and stop the darkness from emanating, Sora convinces her to stay put, not wanting her to get hurt and also joking that she would be in his way; he also acknowledges that, since their hearts were one, they will always be together. During this conversation, it was revealed that Kairi's voice brought him back from the darkness. Kairi gives in and gives Sora her lucky charm, which doubles as the Oathkeeper.

“	Remember what you said before? I'm always with you too! I'll come back to you—I promise!	”
—Sora to Kairi

In the game's final cutscene, she appears on a section of Destiny Islands after Sora's final battle with Ansem, Seeker of Darkness, likely confused. Sora runs up to her, a little too late as the world is breaking apart, restoring all the previously destroyed worlds. Just before she is sent back, Sora promises that he will come back to her as soon as he finds Riku and King Mickey. She is then transported back to Destiny Islands without him, wistfully watching the island regenerate around her with Sora's goodbye still fresh in her mind.

After the worlds are restored, Kairi visits the Secret Place, looking at the pictures that she and Sora had drawn over the years. Once she sees the picture that Sora had drawn of him giving her a Paopu Fruit, she is moved to tears and adds to it; the picture now depicting herself and Sora exchanging two halves of a Paopu fruit.