Sora, Donald, and Goofy find themselves at the foot of a snowy mountain, with a kingdom called Arendelle across the sea. Suddenly, the sea begins to freeze, and it quickly becomes completely covered in ice. Sora sees a woman running across the water, turning it to ice with each step, running towards the mountain. They go to confront her, where she reveals that her name is Elsa, the queen of Arendelle. They try to talk to her, but she insists on being left alone. They begin to argue, causing Elsa to accidentally shoot some icicles at them. Before the trio can speak to her, some Heartless appear and attack. They defeat the Heartless, but Elsa runs away, creating a wall of ice to block their path.
As the trio wonders what to do next, they are confronted by Larxene, who now has golden eyes as a member of the true Organization XIII. Just like with Marluxia, she re-introduces herself to Sora and friends, who forgot about her after Castle Oblivion. She explains that the Organization doesn't intend to hurt Elsa, but they can't have Sora meddling either, so she uses her lightning powers to transform Elsa's wall of ice into a labyrinth, which she traps them in. After escaping the labyrinth, Sora and the gang make their way to the top of the mountain, where they encounter Elsa again. She is full of doubt at first, but she decides to embrace her true self, which fills her with self-confidence. As she does, she creates a palace of ice with her magic.
Sora and friends try to enter the palace, but Larxene stops them. She explains that Elsa might be one of the new Princesses of Heart, but they can't know for sure yet; due to her doubt, Elsa may not have a heart of pure light, and the Organization's goal is to find out if she does. Larxene says that the nature of Elsa's power depends on her perception of it; if she sees her powers as dark, she will embrace the darkness, but if not, she will be filled with light. Sora states that he won't let Elsa fall to darkness, but Larxene insists that she must decide on her own, so she uses her lightning to push the trio off the mountain.
Shortly after Sora and the gang wake up, an avalanche begins to descend from the mountain. They attempt to escape, but it manages to overcome them, knocking them unconscious. Sora is woken up by what appears to be a snowman, but by the time he gets up, it's already gone. They head out to a clearing, where they encounter the snowman with a man and a woman. The woman says that the snowman's name is Olaf, and they introduce themselves as Anna and Kristoff, along with the latter's reindeer Sven. Anna tells Sora that Elsa is her sister. She explains that, when they were little, they were very close, but Elsa grew increasingly distant from her over time. Eventually, she accidentally lashed out at Anna with her ice magic, which is what caused her to flee. Hearing this story, he is reminded of Riku, who tried to push Sora away from him when he took on the form of Ansem, Seeker of Darkness.
Kristoff and Sven return to tell them that Olaf broke apart, so they search for his pieces. After putting him back together, some Heartless appear. Sora, Donald, and Goofy stay behind to fight them while the others go on ahead. When she reaches her sister's palace, Anna tries to convince Elsa to come back, but she refuses. Like before, she explodes with a burst of rage, lodging an icicle into Anna's heart. Shortly after Sora and friends reach the palace's entrance, a big snow monster named Marshmallow appears and throws Anna, Kristoff, and Olaf out. Sora and the gang hold off Marshmallow while the others escape, but he manages to corner them on a cliff. After destroying the small part they were standing on, they plummet back to the base of the mountain.
Shortly after falling down, the trio sees a redheaded man named Hans carrying an unconscious Elsa. They see darkness emanating from him, so they try to stop him. They lose sight of the man, but they encounter Marshmallow again. He ignores them and simply calls out Elsa's name. Hearing this, Sora stops him and explains that they're both trying to save her, so Marshmallow agrees to join them. They catch up to Kristoff, so they have Marshmallow stand back in order not to scare him. Kristoff explains that only an act of true love can undo the ice magic, which is slowly freezing Anna's heart. He took her back to Arendelle to see Hans, who is supposedly Anna's true love. Sora is surprised that Kristoff is not the man she loves, much to his embarrassment. He runs off to find Anna, and Marshmallow rejoins the group.
On the frozen sea, Anna, who is nearly completely frozen, sees Kristoff. She tries to go over to him, but then she sees Hans draw his sword in an attempt to kill Elsa. She jumps in his way just as she freezes. The magic ice is so hard that it shatters Hans's sword, as well as sending him flying back. Darkness begins to consume Hans, and that darkness envelopes Sora and friends. They witness Hans transform into a monstrous, wolf-like Heartless called Sköll, which they then fight. Upon defeating him, Sköll explodes in a burst of dark energy.
After the battle, the group sees Elsa sobbing over the frozen Anna. This act of grieving constitutes a sisterly form of true love, proving that love needn't be romantic to undo the magic. Anna turns back to normal, much to everyone's relief. Sora, Donald, and Goofy try to join the reunion, but Larxene stops them. She observes that both Anna and Elsa's hearts have been filled with light, meaning that both of them are Princesses of Heart. Larxene repeats what Marluxia said: the Organization plans to use the princesses as a backup in case Sora fails to find the other Guardians of Light; therefore, if he wants to keep them safe, he should find the other guardians. She says that the Organization has already found all thirteen Seekers of Darkness before vanishing. Meanwhile, after realizing that her love for Anna is what undid the ice magic, Elsa then uses that magic to undo the curse on the whole kingdom. With that taken care of, Sora and friends decide to return to the Mysterious Tower.
Riku and Mickey reach the tower shortly before Sora, Donald, and Goofy do. Sora tells the others what Larxene said about already having found all the Seekers of Darkness, but Mickey doubts her words. Sora also tells them about the Organization's search for the new Princesses of Heart. He notes that Kairi still has her powers, meaning that she must still be a princess. Goofy reports that Ventus's heart is inside Sora, which is confirmed by Ansem the Wise's data. The problem is that, even if they know where Ven's heart is, they don't know where to find his body; only Aqua knows that, so they can't save him until they get Aqua first. Yen Sid instructs Sora to keep searching until he can use the Power of Waking; meanwhile, Riku and Mickey need to return to the Realm of Darkness.
Meanwhile, at the Keyblade Graveyard, Marluxia and Larxene are talking. Larxene wonders why Master Xehanort would accept them back into the Organization when they betrayed him (as Xemnas) in the original one. Marluxia says that to Xehanort, they are nothing more than puppets; as long as he gets his thirteen vessels, it doesn't matter what they do. A voice speaks behind Larxene, and she turns around to see Demyx, who has also rejoined the Organization and consequently has golden eyes. Demyx says that he was benched and replaced with a replica, much to Larxene's amusement. Marluxia explains that the replicas have developed significantly since the last time they tried to use them; the new replicas will be indistinguishable from real people once Vexen is finished with them.
Hearing that the replicas are still incomplete, Larxene realizes she was wrong when she told Sora that they already have all thirteen members. Xemnas appears and tells them that even if what Larxene said was wrong, it will benefit the Organization, since it will make the Guardians of Light panic and rush to complete their mission. When Larxene asks him why Demyx is back, Xemnas goes on to explain why he chose the members of the original Organization. Members 1-6 were Ansem the Wise's original apprentices, and 7 and 8 joined soon afterwards. 13, of course, was a Keyblade wielder, so it is obvious why Xemnas chose him. Just as he is about to explain why he chose 9-12, the only missing member of that group, Luxord, appears, also with golden eyes. He tells Larxene that he was brought back into the Organization by Xigbar, who is trying to find the black box. At Luxord's insistence, Xemnas finally reveals why he chose the four of them: because the legacy of ancient Keyblade wielders rests within them...
