From Floors 2 to 6, Sora can choose to visit Wonderland, Olympus Coliseum, Agrabah, Monstro, and Halloween Town in any order. This is assuming he's visiting them in the order he does in the first game.
Sora and the gang are back in Halloween Town, where Donald plays the tough guy and says nothing will scare him. When Jack Skellington leaps out to welcome them, of course he gets frightened. Jacks attempts to welcome them once again, but he explains that they've had a bit of a Heartless problem. It turns out to be a self-demonstrating issue, as a bunch of them show up. With Jack's help, Sora, Donald, and Goofy destroy the Heartless. After the battle, Jack explains that he was headed to Dr. Finkelstein's lab to ask him why the Heartless are attacking. Donald doesn't trust Jack, who pulls a small prank on him before they continue.
In the lab, Dr. Finkelstein says that he invented a potion that would allow people to see their true memories. He explains that memories are distorted within one's mind. The way one perceives an event in the past is different from how it actually occurred, and this results in a warped view of the past. Finkelstein says that he created the potion so people could see how the world truly is. Unfortunately, as soon as he sniffed the scent of the potion, Heartless started showing up. He says that he wants to continue his research to figure out what went wrong, but the potion vanished. He assumes Sally took it, so he sends Sora and Jack to find her. Sora, intrigued by the concept of true memories, decides to honor the doctor's request.
The group heads to the Spiral Hill, where they find Sally. She explains that she took the potion because she was afraid of its power. If even a small whiff of its smell can summon so many Heartless, she fears that something horrible could occur if someone actually drank it. Jack, of course, is excited by the possibility of "something horrible" happening. Sally is reluctant to hand it over, but suddenly Oogie Boogie shows up, tackles her, and steals the potion. The boogeyman ponders what would happen if he drank it, hoping it would help him spread despair all across Halloween Town. Oogie runs off, and the group pursues him to his manor.
They confront Oogie Boogie in his torture chamber, where he chugs the whole potion. Oogie acts like his usual cocky and confident self at first, but then he begins to tremble, stating that something horrifying is emerging inside of him. Oogie gets so terrified, that he even tells his nemesis Jack not to get too close out of fear for what could happen to him. Unfortunately, it's too late; the potion overtakes him and turns him hostile. Sora manages to destroy him, and they take the bottle with them.
Back in the lab, it turns out that there are still a few drops of the potion left. Goofy suggests that Sora drink it, but he decides not to, stating that he told Axel that he would learn the truth on his own. Finkelstein says that Oogie must have found his true memories, but that learning them caused him to become emotionally unstable. Sora asks what would happen if he found his true memories. Finkelstein says that something even more horrifying could happen, but he isn't sure. Jack asks Sora if the doctor's words scare him. When he affirms this, Jack says that fear is good, since it encourages one's heart to try new things. With that, they bid farewell and leave Halloween Town.
The trio find themselves back in Castle Oblivion, where they meet Larxene for the first time. Donald correctly guesses that she is in cahoots with Axel. Larxene tells Sora that he is remembering his true memories, bringing Finkelstein's words back to mind. She tells Sora that the blond girl will be heartbroken once she hears that Sora forgot her name, prompting him to ask Larxene if she knows her. Larxene confirms that the mysterious girl is actually in Castle Oblivion and then attacks Sora. She knocks him so hard that Kairi's good luck charm falls out, but it strangely looks different than it did before. When Sora sees it, he can't remember what it is, causing Larxene to taunt him over it. She tells Sora to think clearly to recall how he got it and from whom. Sora slowly begins to remember the mysterious girl's name, uttering the first two syllables: "Na...mi..." At further urging from Larxene, Sora finally recalls her name: Naminé.
Larxene tells Sora that Naminé was the one who gave him the good luck charm and proceeds to take it, guilt-tripping him over forgetting her name. When she threatens to destroy the charm, Sora goes into a rage and attacks her, causing her to drop the charm. He picks it back up and proceeds to battle Larxene. After testing him for a while, she hands him a new world card and vanishes, but Sora angrily slashes at the air for several seconds, causing Donald, Goofy, and Jiminy to worry about him. When they finally get through to him, Sora asks himself why it took someone like Larxene to recover his memories of Naminé.
Larxene goes back to report to Axel, who taunts her over having lost the battle. Suddenly, another Organization member named Vexen shows up. He proceeds to chastise Larxene for letting herself lose to someone like Sora. Vexen says that he isn't as confident as them that Sora is worth their time, but that he is willing to test him with one of his experiments; Vexen, who also happens to be one of the higher-ranked members of the Organization, is a scientist, who apparently has a new subject that he wishes to try out. As they plot, a familiar figure steps into the room. Meanwhile, Sora is rushing towards the next world, wanting to rescue Naminé from the Organization as quickly as possible...
