After fighting some Heartless, Sora realizes that the sea is turning to ice and sees Elsa from a great distance running through the waters. Wondering what happened, Sora, Donald, and Goofy chase after Elsa to find out more about her emotional state. Annoyed by the group's chatter and confrontation, Elsa loses her temper and accidentally reveals her magical abilities, shocking Sora and her friends. Drawn by Elsa's fear, the Heartless appear, prompting Sora and her friends to protect her. After defending herself against the Heartless, Elsa reunites with Sora and the gang. Just as a Heartless is about to ambush Sora from behind her, Elsa defeats him with an icy blast, revealing the strength of her powers. Sora is impressed by this, but Elsa becomes apprehensive and creates a huge wall of ice between herself and Sora's group. Elsa flees to North Mountain as Sora tries to get closer, stopped by the barrier. Larxene appears before Sora and the gang, exclaiming the possible use of Elsa for the actual purpose of Organization XIII. To avoid any possible interference from Sora, Larxene breaks through the ice wall with her electrical powers, then uses the broken ice to form a large maze, trapping Sora, Donald, and Goofy.
After going through twists and turns of the glacial maze, Sora and the gang finally escape through a mysterious portal. The portal transports the group to the side of Mountain Top. They agree to reach Elsa in the North Mountain, before Larxene's malicious influence can reach Elsa. While climbing the mountains, Sora and the gang finally catch up with Elsa, embracing her new lifestyle by creating a beautiful ice palace (during the Let It Go musical). Sora and the gang are left speechless and captivated by the beauty and grandeur of the ice palace. Sora decides to greet Elsa, only to deal with Larxene one more time. Larxene admits her interest in Elsa, with the possibility that Elsa is one of the New Seven Hearts. Interested in another possibility, Larxene wonders if Elsa and her abilities have ties to the dark, increasing her interest in Elsa. Sora retaliates, claiming that Elsa would never trust the dark. As soon as she seems to find out, Larxene launches the trio down the mountain with a powerful electric wave.
After falling off the mountain, Sora and the gang find themselves under North Mountain. Just as Sora plans to return to Elsa's palace, the gang is greeted with an avalanche. Goofy uses his shield as a sled to escape the avalanche, only to be ambushed by three Frost Serpents. After defeating the three Big Heartless, Sora and the gang are attacked by another avalanche.
After regaining consciousness from the avalanche, Sora briefly meets Olaf. Determined to talk to Elsa again, Sora, Donald and Goofy begin to ascend the mountain. When they arrive at a frozen pond, Sora recognizes Olaf walking with Anna, Kristoff, and Sven. Realizing that both groups are looking for Elsa, they decide to find her together. Sora and Anna have a long conversation about Elsa, and she explains how the two sisters parted ways (via a musical performance of Do You Want to Build a Snowman). Kristoff quickly rushes in, imploring the group to search for Olaf's missing parts, as he has fallen apart. Upon completing Olaf's body, Kristoff explains that his group crashed into a group of Heartless. At the mention of the Heartless, they appear once more. Sora urges Anna, Kristoff, Sven, and Olaf to leave, while Sora, Donald, and Goofy face a ruthless Horde.
Climbing the cliffs of the winter mountains to catch up with Anna and others, the trio once again arrive at North Mountain and Elsa's ice palace. Inside the ice palace, Anna talks to Elsa in hopes of ending eternal winter, but Elsa continues to emphasize her lack of control over her powers. Elsa loses control and accidentally hits Anna with her ice magic. Sora, outside the palace, feels this with pain in his heart and I believe that something terrible has happened in the palace. Just as Sora is about to enter, Elsa's bodyguard Marshmallow ejects Anna, Kristoff, and Olaf from the palace. The bulky bodyguard pursues the group, causing Sora to separate from Anna. Sora, Donald, and Goofy decide to fight Marshmallow. He corners the trio on a cliff and hits the ground, causing the edge of the cliff to collapse and they fall into the abyss. At the foot of North Mountain again, Sora, Donald, and Goofy regain consciousness and climb back up, still intending to speak to Elsa. On the way, they see Hans carrying Elsa unconscious. The trio feel that the man gives off a dark and evil aura and decide to pursue him.
While chasing Hans, they run into Marshmallow, who is chasing Elsa for her safety. Both harboring the same intention, Sora decides to form an alliance with Marshmallow and head towards Arendelle. Sora catches up with Kristoff and Sven, noticing Anna's absence. Kristoff explains that Anna was attacked by Elsa's ice magic and that only an act of true love can save her from freezing, an act performed by Anna's true love, Hans. Realizing the trio's confusion, as they assumed Kristoff to be Anna's love interest, Kristoff dejectedly clarifies his role as just a guide. A vicious snowstorm blows and darkens the city, causing Kristoff and Sven to run back to the kingdom in fear for Anna's safety. As Marshmallow points to the city, the group realizes that Elsa might be in danger too and they run into the storm.
The trio and Kristoff find Anna, walking weakly, in the frozen fjord. Just as Anna and Kristoff are about to reunite, Anna sees Hans preparing to kill Elsa from behind. Faced with a quick choice, Anna rushes to protect Elsa from Hans and her body completely turns to ice. The strong impact between Hans's sword and Anna's frozen body knocks Hans unconscious. Darkness begins to emit from Hans's heart, sucking Sora, Donald, and Goofy into a dark portal. Inside the portal, a huge heartless, Sköll, appears before them as Marshmallow joins the fight. Upon defeating Sköll, his dark ball form explodes, emitting a strong wave of power. Marshmallow leaps forward to protect the group from harm, but the four of them fall into an abyss.
Sora and the gang wake up in the frozen fjord in Arendelle. Sora watches Elsa cry over Anna's frozen form as Kristoff, Sven, and Olaf remain solemnly silent. However, the frozen Anna begins to thaw, much to everyone's surprise.
Before the now ecstatic trio can intervene, Larxene stops time and watches the sisters. Larxene informs Sora that if they fail to reunite the seven Guardians of Light, Anna and Elsa's role as the New Seven Hearts will draw the sisters into the War of the Keyblade. Sora tells Larxene to leave the innocent people behind, and only asks Sora to hurry up gathering of the guardians to avoid casualties. Sora taunts her saying that the Organization still has few members, but Larxene claims to be prepared, surprising them. When Larxene leaves Arendelle, world time resumes.
As Anna and Elsa embrace, Sora, thinking of the Real Organization XIII's plan for the two of them, begins to worry for their safety. Goofy and Donald comfort Sora, assuring him that the strength of the two sisters is sufficient for his safety. The sisters reconcile, learning that Anna's sacrifice was the act of true love necessary to save themselves. Elsa discovers that love is the key emotion to control her magical abilities, allowing her to undo the eternal winter that curses Arendelle. As the warm sunny weather returns, everyone rejoices.
Sometime after Xehanort's defeat, Anna, Olaf, and Kristoff have gone sledding when Elsa forms an ice ramp for her safe landing and Marshmallow catches Olaf and his body parts.
- Despite Elsa unfreezing the world at the end of the storyline, Arendelle's winter exterior remains for the remainder of the game.
- Arendelle is the second Disney world in the Kingdom Hearts series to feature all of its home characters portrayed by their original actors from their original appearance in the movie, the first being Deep Space from Kingdom Hearts Birth by Sleep.