After their visit to Twilight Town, Sora, Donald, and Goofy called Riku and Mickey up on the Gummiphone and let them know what Hayner's group said. The pair headed to the laboratory in Radiant Garden straightaway.

Mickey, who had just arrived with Riku, leapt straight into Ansem the Wise's arms and Ansem caught him and took him in an embrace.

"Gosh! I didn't think I'd ever see you again!"

"King Mickey, my friend. How I've longed to converse with you once more, like old times. I had thought it but a hopeless dream." He then turned to Riku. "And Riku, I cannot express how sorry I am to you."

"That's okay. We're all capable of losing ourselves to the darkness. I'm glad you're home again."

Everyone looked on happily, and Dilan and Aeleus couldn't help but tear up.

Mickey's smiling expression then changed to a more serious one. "I'm sorry. I wish we had more time to reminisce, but we'll have to save it for another time. There's something important we need to ask you about."

"It's about my apprentice, Xehanort. He has returned. And he was trying to recreate Roxas's heart out of data, using the virtual Twilight Town."

Riku recalled Ansem's Code:

I have discovered a unique heart inside of Sora's. It has resided in his heart for a very long time—his entire life, in fact. This is a truly astonishing discovery. While this heart has now melded with Sora—grown silent and indistinct—Sora retains the memories of it. The memories have been compartmentalized—placed in their own "box," so to speak.

The silver-haired boy addressed him, "The data you left inside of Sora's heart while he was asleep. You knew about Ventus?"

"At last, the Keyblade's chosen one."

"Who are you talking to? Me? Or Sora?"

"To half of Sora, of course. You reside in darkness. What I need is someone who can move about the realm of light and destroy Organization XIII."

"Yes. While Sora slept, Naminé was repairing his memory. And she found memories that didn't belong to him that had been sleeping in his heart for a very long time. That is how I discovered Ventus's heart."

"Xehanort is trying to bring him back to recreate another Keyblade War," said Riku.

"I knew he must have been up to something all those years ago. It was the same with Subject X."

Riku, who once wore his apprentice's face, looked up at his old comrade. DiZ. Darkness in Zero. In a way, Ansem the Wise could be considered the Organization's founding member. Number 0. He had given Mickey and Riku black coats, too.

"The Xehanort you knew was just a possessed version of a Keyblade wielder named Terra."

"Terra...?"

"Yeah. Xehanort possessed him and took over his heart."

Ansem stopped to think about that bit of information. "While I was repairing his memories, I observed two hearts inside him, just like with you, Sora. That is why i stopped my experiments on him. After his memories began to return, his personality completely changed."

Mickey nodded. "Yup. Xehanort fused his heart with Terra's."

"Then the young man I first met..."

"That must have been Terra," Riku asserted.

Ansem was stunned. "Then...he did not really betray me...?"

"No," said Mickey. "Xehanort just took over his body."

The wise sage seemed sad, yet extremely happy as well. "Terra... I would like to meet him again some day."

Riku wanted Ansem to meet him, too. "We're trying to find him and his friend Aqua right now. Do you have any clues for us?"

"Oh, Aqua..." the wise man lamented.

"You know her!?" Riku and Mickey said in unison.

"I met her in the Realm of Darkness. She said...she knew someone would be coming for her. But Xehanort plunged her into the watery depths."

"No..." Mickey hung his head in shame. "Then we're too late..."

In the realm of darkness, at the edge of the water, Riku and Mickey were locked in battle with a Demon Tower. It wasn't going well; when Riku was distracted by Mickey in trouble, he was swatted across the
beach.

"Riku!"

The swirling mass of Heartless didn't miss the opening Mickey left in his defenses as he started to run for his friend. The Demon Tower swallowed the king up, sending his Keyblade tumbling to the ground.

"Mickey!" Riku shouted from the sand.

But the Demon Tower moved to block his path, Mickey still in its clutches. This battle wouldn't be easy.

"Get lost!"

Riku attacked the Demon Tower with all the power surging within him. The Tower itself was a huge mass of smaller Shadows merged together. It swirled about like a vortex, occasionally rising up in a huge column that swiped at Riku. He wasn't about to let it defeat him, though—he would save Mickey from the darkness that had taken hold of him.

The Heartless were no match for Riku and scattered, finally freeing Mickey from his prison. Riku tried to run over to the king, who was lying on the sand.

"Mickey! Wake up!"

The same thing happened to me last time. He's asleep. And he won't wake up unless I use the power of waking.

Riku decided he had no choice. He'd have to dive into Mickey's heart.

Sora, Donald, and Goofy were looking for the next world in the Gummi Ship when a familiar ringtone suddenly filled the cockpit.

"Huh?" Sora pulled the phone out of his pocket.

"Sora, somebody's callin' us on the Gummiphone," said Jiminy Cricket as he hopped onto Sora's shoulder to better see the screen. Donald and Goofy crowded in from either side, eager to find out who was calling, and Sora hit the button.

"We got baaad news!" Dale squeaked from the screen.

Chip quickly pushed Dale off to one side. "We've totally lost contact with the king and Riku! They're all on their own in the realm of darkness!" he reported.

Everyone on the Gummi Ship cried out in shock. "Whaaat?!"

"See? I knew we shoulda gone!" Sora complained.

"Chip, how do we get to 'em?" asked Donald.

"Now we can ask?" Sora said, reminding him of what happened the last time this came up.

As always, Goofy kept them focused. "It's not like we can use that big door anymore. It's completely gone."

"Yeah, we closed it after beating Ansem," Sora said, now directing his irritation at Goofy.

Jiminy paused thoughtfully. "And we certainly can't ask the king or Riku."

"'Cause you wouldn't let me ask," Sora snapped back.

Before they could argue further, Dale interjected. "Only King Mickey can open a door to the realm of darkness."

"Huh?"

"It's because he has a special Keyblade of darkness. He figured out how to make it open the way," Chip told everyone as he struggled with Dale to stay in front of the small screen.

"Oh…" Sora contemplated the situation for a moment.

"Gawrsh, what'll we do, then?" Goofy asked dejectedly.

Sora turned his eyes forward.

If the king's Keyblade can open doors to the realm of darkness…

"May my heart be our guiding key. It'll show us the way," he said, then called his Keyblade to his hand and pointed it out before them. The Keyblade began to emit light, and just as when they opened the way to Olympus, a portal appeared within the Ocean Between.

"A gate!" they exclaimed.

"But where does it lead?" Sora asked.

"It doesn't matter! Go!"

"Hurry, Sora!"

Donald and Goofy urged him.

"Okay," Sora replied, then took the helm of the Gummi Ship and guided them through the gateway.

The trio arrived on a beach among clear skies, blue seas, and the sound of waves—the Destiny Islands, the very same small place where Sora and his friends' journey had begun.

"Why do you think that gate took us here?" Sora wondered as he, Donald, and Goofy walked along the beach. Nothing appeared to be any different than ever—except for what he'd just spotted lying in the sand.

"A Keyblade?" He picked up the weapon, which must have belonged to someone else.

"It looks so old," Donald commented.

Sora inspected every inch of the Keyblade—he'd never seen one like this before. The color of it was quite dark, and he didn't recognize the shape on the key chain.

"How did it end up here?" he murmured, turning it this way and that.

"Hmm, maybe it's another guiding key," suggested Goofy.

"Sure, but to guide us where?"

Sora took the Keyblade in hand and listened to where his heart told him to point it. A beam of light gathered at the tip of the blade and headed straight into the entrance to the Secret Place. As the light faded away, it revealed…

"A door!"

"Let's go."

Donald and Goofy were raring to go, but then Sora stepped in front of them and said, "Not you guys."

Donald and Goofy were shocked. "Huh?!"

Sora approached the door alone. "The realm of darkness—it isn't safe for you."

Donald and Goofy weren't going to take this sitting down, though.

"Forget it. I'm going."

"Yeah. You can't make a whole pint without us."

Sora turned back to face them. "Come on, guys, think about it. Even the king and Riku struggled in the realm of darkness. Someone needs to stay out here, just in case. If something happens to the rest of us, you two need to carry on."

Donald and Goofy looked crestfallen.

"Sora…" Donald said softly, and then more angrily: "Stop it!"

Goofy wasn't ready to give up, either. "We understand, but we don't want you goin' someplace dangerous on your own."

Sora only gave them a smile. "Thanks, guys. But I'll be fine. I'll make sure Riku and the king are safe. Trust me." He punctuated the reassurance with a heroic pose.

Goofy and Donald looked at each other, then turned back toward Sora.

"You promise to be good?"

"And come home nice and safe?"

"Yeah," Sora said with a firm nod to his worried friends.

Riku stood on a familiar beach. The Dark Margin.

"Wait a second...am I back in the realm of darkness? What's going on?"

Suddenly, Riku spotted him.

"Mickey!"

The king was completely immobilized, trapped inside a pitch-black mass. Upon closer inspection, he was asleep and his Keyblade lying on ground nearby.

"Wait. I've seen something like this before."

Is he trapped in a nightmare like Sora was?

Then, from within the darkness stepped forth a figure hidden by a swirling shroud.

A Nightmare?

"This Keyblade…" The figure picked up Mickey's fallen weapon. "Mickey… You're too late."

"Aqua?" Riku said, almost to himself.

The woman who turned back to face him. She had pale-blue hair and golden eyes—the golden eyes of someone consumed by darkness.

"What happened to you?" asked Riku sadly.

Aqua's grip tightened around the Keyblade. "You abandoned me, that's what. Left me in this shadow prison for more than a decade, knowing what it would do to me…"

"I'm sorry. It's all my fault." Mickey's face was filled with sorrow, even as he talked in his sleep.

Riku was now convinced that he was in the middle of his friend's worst nightmare.

"I reached this shore after endless wandering," Aqua hissed as she walked over to the edge of the water. "Waited forever for help to arrive. But no one ever came. I lost my Keyblade. Had no means of fighting my way back through the Heartless. You should have known I was stranded."

As she spoke, she walked over to the edge of the water. All Riku could do was watch.

"Do you have any idea how lonely it is here? How frightening it is to have no one? All that's left in my heart is misery and despair…and now, you can share it!" she shouted, turning to face him.

Riku stepped forward. "There's no need," he said. "Got my own."

He closed his eyes for a moment, sensing the presence of another version of himself. Riku, and who he used to be—his Replica.

And this Replica was with him now—had been with him all along.

Will you come with me? I know, I don't have to ask. Where one of us goes, the other follows. You're the darkness in my heart, so you'll always be with me. Like a shadow. I wouldn't be who I am now without you.

Riku opened his eyes and focused them on Aqua.

The power welling up within him transformed into a Keyblade. Quietly, he stepped toward the fallen master awaiting him beneath the light on the water.

Aqua attacked him with magic, but he deflected the spell and chased after her. Aqua then swung her Keyblade at Riku and used the recoil of her blade against his to put some distance between them.

Riku struck with his Keyblade again and again, putting every ounce of strength he had into each blow. But no matter how many Shadows he destroyed, more arrived to take their place. He wasn't getting anywhere like this.

"Sora…" Riku didn't know why the name left his mouth as he gasped for breath.

A door opened in the sky, releasing a blinding light and—Sora himself.

He flew down and dropped to the ground next to Riku.

"I made it!" Sora exclaimed with a smile, which Riku returned.

The connection between the two took visible form as a brilliant halo around them. Their Keyblades merged, producing a powerful torrent of light.

Just as it was during the Mark of Mastery exam, the two were in different worlds. Riku was in Mickey's dream world facing off against a Nightmare, while Sora was in the real Realm of Darkness facing off against Aqua's shadow. But they were able to unite for their ultimate attack.

The Heartless were no match for the devastating blast and scattered, finally freeing Mickey from his prison. Riku tried to run over to the king, but Aqua was hot on his heels. Just before her Keyblade could strike his back, Sora jumped between them and blocked the attack.

"How, Sora?" Riku asked.

Sora showed him the Keyblade he'd found on the Destiny Islands. It was also the one Aqua had once wielded herself—the Master's Defender.

"I…had a little help," Sora replied. "Watch over the king. I've got this."

He turned to face Aqua with the Keyblade at the ready.

"Okay." Riku hurried over to Mickey.

Sora watched him go for a moment, then devoted his full attention to Aqua.

I'm finally meeting her for the first time, but it doesn't feel that way. Not because of the darkness—there's something deep in my heart that knows her.

I have to find a way to stop her here.

Aqua came flying at him, and Sora held her back with his Keyblade. The blow made his hands go numb, and he gritted his teeth against it. With a small smirk, Aqua put some space between them again.

He couldn't afford to go easy, not even a little. Not only had she embraced the darkness, but she was also a Keyblade Master.

Sora charged at Aqua, but just as he reached her, she split into three copies. He couldn't tell which one was real.

He tried magic on the Aqua closest to him, and the copy burst into specks of darkness. He just barely managed to get his Keyblade up in time to intercept a downward slice by another Aqua from the side—just as the third Aqua darted in from behind and knocked him upward.

Sora managed to recover in midair just before he landed. That was apparently what the two Aquas had been waiting for, though, because they were both on him instantly. A spell from Sora made quick work of the attackers, which meant all that remained was the real Aqua. He parried her Keyblade, then used the momentum to get in close and land a solid hit.

Aqua dropped to her knees, clutching her chest.

Light radiated from the Keyblade in her hand as a dark fog enshrouded her body, and Mickey's Keyblade slipped from her fingers before vanishing in a brilliant flash.

Aqua fell onto the surface of the murky water and began to sink.

As Sora watched her sink, the gears in his mind were spinning.

"We know Master Aqua made it as far as the beach that Sora and I once visited, but that's where her trail ends."

Aqua fell in the sea. Was she the one who dropped the Keyblade I found? But then, how did it get to the realm of light?

Wait. I get it now. The Keyblade. It's like Kairi's letter.

Kairi let her letter loose in the realm of light and it found its way to Sora and Riku in the realm of darkness.

Aqua lost her Keyblade in the realm of darkness and it was able to travel to the realm of light."

"She's gone?"

"No. Sora was dragged into the abyss during his exam. And I went in after him. So, I think if we find someone that was really close to Aqua, and they make the dive, they could reach her down there."

Ventus. You want to save Aqua, don't you?

"Still so blind. A Nobody is what's left behind when one gives his heart to darkness. There is only way to bring Roxas back, which is for you to give your heart up as well. Sora, have you finally decided to call upon the darkness?"

"What?"

"Go on, then. The shadows are never out of reach."

"Now, set your heart free."

Having made up his mind, Sora dove into the water after Aqua.

"So…this is the fear and despair that Aqua feels… And now…I feel it, too. Is this…Aqua's heart?" Sora said as he looked around.

As he hovered above Aqua's blue Station of Awakening, he saw that the spot on her heart was black.

So this is what the fear in her heart looks like. I have to get rid of it!

Sora used his Keyblade to cast the darkness away.

The last thing Aqua remembered was Xehanort throwing her into the sea at the Dark Margin. She was sinking deeper and deeper.

"So…this is the end," she said softly, then closed her eyes.

For so long, the waves were the only sound out here on this beach.

Just waves crashing in the darkness. Nothing else. I thought I would never hear anything else again.

No one would come to save me. After all, I couldn't save anyone else. I broke my promise. I failed.

I'm sorry.

I can feel myself sinking deeper and deeper into this darkness. Soon I'll be too far gone, and no one will ever find me again.

"Aqua!"

Suddenly, Sora reached for her.

What was it that she saw? Was it light? Or was it…?

"Sora…"

Aqua reached out to take his hand, and then the world went white.

"Aqua!"

I hear a voice calling my name. Ventus's voice.

"Aqua!"

Terra, too. Oh, they look so worried. And the sky behind them is…blue.

And so bright.

What's happened to me?

"Ven… Terra…"

I say their names, too.

Maybe I can keep my promise after all… I have to, no matter what.

The darkness is behind me…and I'm awake.

"Aqua!"

Sora and Riku peered at Aqua's face. They were on the Destiny Islands with her and Mickey, right at the edge of the waves, as they had been the last time the two returned from the Dark Margin after receiving Kairi's message in a bottle.

Aqua's eyes opened slowly, and she sat up. "It's you…" Confused, she took in her surroundings.

"Thank goodness! You're awake," Mickey said to her.

"Mickey…"

The barest hint of understanding began to dawn on Aqua's face. "Are these…the Destiny Islands?"

"That's right," Mickey replied.

Aqua still seemed a little dazed. "When did they fall to darkness?" she asked, but Riku shook his head and smiled.

"You're in the realm of light."

As Aqua looked up at him, tears began welling in her eyes.

"You're home," said Sora, extending a hand to her.

The tears spilled over, and Aqua wept with joy.

"You're home!"

"Welcome home."

Donald and Mickey ran up and embraced her, Sora and Goofy joining shortly after. Riku hesitated, then slowly joined them, too.

The lonely silence was finally over.

The welcoming sun of the Destiny Islands shone down upon everyone.