dont worry cause its roxas to the rescue

Spoiler warning: Plot and/or ending details follow.
The story of Kingdom Hearts: Chain of Memories takes place directly after the ending of the first installment, Kingdom Hearts. We find Sora, his two friends Donald Duck and Goofy, as well as Jiminy Cricket, walking down a seemingly never-ending path, when suddenly a mysterious man dressed in a black hooded trenchcoat tells Sora, "Ahead lies something you need. But to claim it, you must lose something dear." As they continue down the path, Sora and his companions find a massive fortress called Castle Oblivion. When they enter, they find the mysterious figure.
When Sora and his companions attempt to engage the figure, they find that their abilities seem to have no effect. The figure then explains that at the moment our heroes entered the castle, they forgot every ability they had previously known. This figure continues by creating a deck of cards made from Sora and his friends' memories, and tells them that everything they encounter in this castle will be based on their memories. But the higher they go, the more memories they lose in the process.
Meanwhile, floors below, Riku has somehow managed to return from the the World of Darkness and fights his own inner demons as he battles upward from the basement levels of Castle Oblivion. But neither he nor Sora are aware that they are being targeted by a mysterious group called the Organization.
As Sora ascends the castle, he battles Larxene, a member of the Organization. After battling her, he remembers the name of a former friend of his that he forgot: Naminé. He learns that she is being held in the castle, and ascends the castle, clashing with a clone of Riku that believes itself to be the original. After watching the death of Vexen, another Organization member, Sora learns from Naminè herself that the hooded figure he met earlier is named Marluxia, and is in fact manipulating both of them into being his servants. Forming an alliance with the Riku clone, they fought to the top of the castle and defeated Marluxia. Sora then bid farewell to the Riku clone, who left to find the truth to his existence. Naminè then puts Sora to an unnatural sleep to help him regain the memories he lost in the castle.
Meanwhile, as Sora was fighting his way through the castle, Riku began destroying dark beings he met in the depths of the castle in an attempt to rid himself of darkness. Xehanort, who took over Riku's body in the previous game, attempted to gain contol of Riku again, but was continually thwarted with the intervention of Mickey Mouse. On the way, Riku battled Vexen, his own clone, and another Organization member named Lexaues. Riku then used his dark abilities and noticed that Marluxia had been killed. He was confronted by Zexion, a manipulative Organization member, but embraced his darkness and overcame him. Arriving in Twilight Town, Riku learned that the 'Ansem' who had goaded him earlier was in fact DiZ, an enigmatic man who seemed interested in Riku. DiZ sent Riku to speak with Naminè, but a new foe blocked his way: the clone. After killing the replica in a fierce battle, Riku learned from Naminè that what remained of the real Ansem lived in the bowels of his heart. Riku chose to face him, and after affirming this with DiZ, the odd man loosed Ansem from Riku's heart for him to battle. After successfully defeating Ansem, Riku learned that as long as he had darkness at his command, Ansem would reside within him. He set out on a quest to keep his darkness but remain his own master with King Mickey as his companion.