Sora and the others have found the final Gummi block to take them to Hollow Bastion, where Riku, Kairi and Maleficent wait. Sora is confronted by Riku, who manages to take the Keyblade from him, saying, "Let the Keyblade choose its own master!" With that, Sora loses hope, and Daffy and Goofy, heeding the words of their king, follow Riku now.
Sora wanders about the castle and discovers the Beast. When Belle was kidnapped from the castle, he managed to follow her here without magic, by using his heart. Sora goes with him to rescue Belle, and finds a wooden sword to use. When they do find what they think is Belle, she is revealed to be a heartless. Riku confronts Sora again, and Goofy and Daffy side with Sora, whose wooden sword becomes the Keyblade again as Sora says he has a more important weapon, his heart.
Riku is momentarily dismayed by this, but unleashes a sword of his own, a dark sword. He takes Kairi to Maleficent, and when she reveals her plans to rule the worlds through the heartless, he uses his Dark sword to let the darkness within her rule, killing her. Sora arrives, but cannot lock the keyhole here, as it isn't complete. Riku tells Sora that Kairi's heart is within him, and that he must unlock his heart with the Keyblade to bring her back. He also reveals that he isn't Riku anymore, but Ansem, who was taken over by the darkness in his own heart.
Sora frees Kairi's heart, but the darkness is about to overtake Hollow Bastion. Sora is transformed into a heartless, but Kairi transforms him back with a kiss. Beast finds Belle and the other Princesses, who have been holding back the darkness. Sora arrives, to find Cid, Squall/Leon, Yuffie and Aerith have arrived as well. They say that Hollow Bastion was once their world, overrun by the Heartless and the Darkness. Sora locks the Keyhole, and says he won't rest until he has undone what Ansem and the Heartless have done. The others look sad.
Cid explains that when he does this, the worlds will stay and remain separate, forever. They will never see each other again. Kairi wants to come with Sora, but Sora tells her to stay, because in their hearts, they will never be separated. She agrees, and gives him another Thalassa shell charm. Then it is off to the final confrontation with Ansem. But Riku still has a part to play, for he is the bearer of the dark Keyblade, meant to close the door to darkness and the heartless from the other side. And he's not alone. King Mickey is with him...
But can Sora take on Ansem and show him that he was wrong?
The last book has very few Disney characters in it at all, showing, I suppose, that they really aren't all that menacing. For real menace, you need a manga character (Ansem). But even now the series isn't ended, for there is still King Mickey to find, and Riku to free from the darkness...
As a series, I am not sure how well it works as a whole. The mixture of Disney and manga characters is awkward at best, but the writer manages to make the story work. The artwork... less well. Combine the two, and well... some people love the story, some people hate it. Me, I consider myself in the "eh" category, in that I can take it or leave it. It will never be a great manga obsession for me in the way that Saiyuki is, for example, but it's an okay story and I will continue to read it. If you have a chance to read this without paying for it, like at a library, take it before purchasing it on your own.