[When you finish Sora’s side of the story you get to play as Riku]
Riku wakes up floating in some mist. A voice tells him to stay asleep between light and dark. The voice is trying to convince him to stay in the darkness. But it proposes an option to wake up. A card appears and the voice says “Take it and your sleep ends, as you take the first step toward the truth.” Riku takes the card and finds himself in Castle Oblivion where he uses the card on the door.
The card brings him inside his memory of Hollow Bastion. The voice says “It must be nice being back in your old bedroom. Think of all the memories… ” Riku informs the voice that he would much rather forget these memories since they involve Maleficent. The voice keeps going saying “And you lived here, tempted by the darkness she offered. You cast away your home, your friends, everything… But at leas they gave you a nice room.” After walking around, Riku wonders why he’s not seeing anyone. The voice tells him he’s not meeting anyone because he cast everyone aside when he walked into darkness.
Back in Castle Oblivion the voice tells Riku that the darkness is his weapon and that he should learn to accept it. The voice reveals itself as Ansem. He just wants Riku to surrender to darkness so he can control him again. King Mickey appears as a light to remind Riku that he isn’t alone and that the light will never give up on him. After a fight, Ansem gives a memory card to Riku.
We see Two man in black cloaks inside a dim lit room. One is Lexaeus and the other is Zexion. Vexen appears and asks for an explanation. Zexion picked up two scents in the lowest basement. One of them belonged to a very convincing double of Maleficent. Doesn’t know for sure who the second scent is, but it is very similar to the Superior’s.
Zexion finally identified the scent as Riku. “His existence, it was once doubled in the darkness.” Vexen answers that that must have been why he first mistook him for the Superior. Vexen says Riku appeared in Castle Oblivion after escaping the realm of darkness because his existence resonates with that of another hero: Sora. In Vexen’s eyes, the one that holds true value is Riku, the hero of darkness.
Vexen appears in front of Riku. When Riku asks if he’s with Ansem he says it’s half true. “He is Ansem and he is not Ansem. Perhaps a “Nobody” best conveys the idea.” He belongs to neither the light nor the dark but walks the twilight between. Reveals to Riku that he also stands between the light and the darkness. Vexen fights against Riku to get data on him.
Zexion is suspiscious of Marluxia and Larxene. Lexaeus doesn’t trust Axel because no one can guess what he’s thinking. Zexion says Vexen should take care of this, that his replica is soon to be completed. That’s when Riku comes face to face with a replica of himself made from Vexen’s data. The replica says he’s not like Riku because he embraces the darkness and makes it do what he wants. They fight, but the real Riku wins. When Fake-Riku goes back to Vexen, Vexen asks him if he wants to meet Sora.
Vexen goes to Larxene and Axel to propose his idea of his replica testing Sora. Larxene wants to remake Fake-Riku’s heart so that he has all of the real Riku’s memories to make it more convincing. Vexen doesn’t object. Fake-Riku doesn’t want to, but they still do it.
After a while, Lexaeus informs Zexion that Vexen is no more. He says their problem is Sora, but they can’t get rid of him because their Superior is in dire need of the hero of light.
Lexaeus appears in front of Riku and tells him he is capable of controlling the darkness. If he doesn’t learn to embrace the darkness he will lose both light and darkness and disappear. After fighting, Riku gives in to darkness and defeats Lexaeus. Before disappearing he says “You are the Superior’s…” Riku faints and finds himself floating in darkness with Ansem telling him he can finally see him again and to let him in his heart. King Mickey appears to protect Riku from Ansem.
Zexion senses that Lexaeus is gone. Axel appears and informs Zexion that he fought against Sora and Sora thinks he defeated him. He asks what they had planned for Riku. Zexion says they had wanted to set him off on the traitors, but since Marluxia will be taken care of, he is only a nuisance now.
The castle shakes and Riku senses one of the scents has died. Zexion appears and informs him that Marluxia, the keeper of the castle, has been defeated by the Keyblade master. He tells Riku that if he faces Sora like this, Sora will have no choice but to defeat him since he has darkness in him and Sora’s mission is to get rid of darkness. He then gives Riku a card of his home.
Inside his memory, Riku keeps seeing his friends, but they disappear as soon as he gets close to them. Zexion appears and tells him it’s because all that’s left in his head is dark memories. He then reminds him how he’s the one that destroyed the islands. Sora appears and throws a beam of light on Riku, which throws him on the ground. “how can the light hurt you? Riku… Have you really become a creature of the dark? You’re not Riku anymore… You’re just a pawn of the darkness.” Then shines a bright light. Riku is falling in the light. Kairi appears and tells him “You can’t fade. There’s no power that can defeat you. Not the light, not the dark. So don’t run from the light, and don’t fear the darkness. Because both will make you stronger.” While Kairi is talking, a transparent figure of Naminé appears next to Kairi and talks at the same time. Riku wakes up and defeats Zexion.
In the real world, Zexion wonders what Riku is. “No one’s EVER worn the darkness the way he does! It’s impossible!” Axel and Fake-Riku appear in front of Zexion. Axel to Fake-Riku: “Wouldn’t you like to be real? All you need is the kind of power that the real Riku doesn’t have. If you can get that, you can be a new person; not Riku, nor anybody else. You won’t just be a copy of someone. You will be unique, your OWN self.” Zexion starts panicking while Axel keeps talking to Fake-Riku: “You know, he’s as good a place to start as any.” Fake-Riku grabs Zexion and seems to absorb his darkness, or just melt him.
Back in the castle, Riku hears Ansem say that he has now a grip on his heart because he let in the darkness. Riku tries to protest, but Ansem proves to him he’s starting to have control by keeping Riku from moving. The light ball that is Mickey enters Riku and interferes with Ansem. Mickey then appears behind Riku, for real. Mickey explains that he was able to find his way to Riku thanks to a card. He says that the card seemed to think it’s place was to be with Riku. The card is of Twilight Town. Riku enters the world and Ansem appears. Ansem wants to fight, but Riku knows it’s not the true Ansem because of the scent. He understands that this being is the one that guided him in the beginning. The fake Ansem transforms into another person and he introduces himself as DiZ. He wants Riku to choose. He tells him he stands between light and darkness. That he walks in the twilight. He says Riku will soon meet Naminé and will need to make a choice. Riku finds himself in front of the gates of a mansion when Fake-Riku appears behind him. He tells Riku that he thought by finding new strenght he would finally be able to be someone that is not Riku. But he’s still empty. He decides to fight against Riku so that there’s only one left. After being defeated, he says he’s not afraid of death because he was never real. He wonders what happens when a fake dies, where will his heart go?
Once back in Castle Oblivion, Riku finally meets with Naminé and sees Sora asleep inside the bubble. Naminé explains to him everything that happened. She tells him he has a choice to make. That even though Ansem is currently at bay, he will eventually take hold of Riku again. She can put a lock on his heart so that Ansem will never come out from inside him. She tells him that if he chooses that, the darkness will be sealed away as well. He’ll stop remembering the darkness and go back to how he was. Riku chooses not to lock his heart. Once he gets out, Mickey welcomes him and says he heard from DiZ about his choice. Riku asks Mickey if he knows him and Mickey says that he’s not sure but he has a feeling he’s met him somewhere. DiZ gives a black cloak to Riku so that he can hide from the Organization. He says they use the cloaks to protect themselves from being devoured by darkness. Even the Organization cannot rule the darkness. He then gives him a card that will draw out the darkness from his heart so he can finish his business with Ansem.
Riku decides to go fight Ansem alone, but asks Mickey to destroy him if Ansem wins. Mickey refuses and promises him that whatever happens he’ll be right there to help him. Riku fights against Ansem and wins. He can still feel a faint glimmer of Ansem inside him and thinks his darkness still has a hold of him. Mickey tells him that his darkness is his own. That spending time with him made him realize that light and dark could work together and wonders where that road will lead. Riku agrees to Mickey going on that road with him.