Sora had just beaten his friend Riku, who was possesed by Ansem, the Seeker of Darkness. He also found out that Kairi's heart was resting within him. They were about to seal the keyhole when...
"Huh? What the? My keyblade won't work!" Sora exclaimed, at the shock of Donald and Goofy.
"It won't work! The keyhole's not finished yet!" Goofy exclaimed. "What can we do?" Sora said, unsure. Goofy then turned to the lifeless body of Kairi. "Maybe we gotta go wake Kairi up."
"But... how?" Sora questioned the two, shaking their heads. The brunette eventually noticed the Keyblade that Riku-Ansem used to nearly kill him. He slowly walked up to it and picked it up. 'A keyblade that unlocks people's hearts... I may have to make some sacrificing.' Sora quietly thought to himself.
'But first...' Sora thought again, looking at the lifeless body of Kairi. He gently put down the keyblade and quietly summoned his trusted Kingdom Key into his right hand. He then walked up to Kairi's body, kneeled down and gently put his Kingdom Key on her right hand. "Take care of the worlds." Sora quietly whispered to her. He then kneeled up and picked up the other Keyblade.
"Sora?" Goofy asked him in worry. "Sora, don't do it! We have other ways of waking Kairi up!" Donald shouted to him.
"Donald. Goofy." Sora quietly said. The two animals tilted their head in confusion. Sora turned around and the two saw him tearing. "Take care of Kairi *sob* and train her, *sob* okay?"
Donald and Goofy nodded at him, but he immediatly stabbed the Keyblade at his heart, a single tear comming out. Eventually, the keyblade dissipated, showing six hearts, assuming it is the Princesses' hearts. Meanwhile, with Sora... Kairi's heart was released from Sora and he was fading away...
"SORA! SORA!" Donald yelled and ran at him, and meanwhile, Kairi's heart entered back in her body, and the first she saw after she opened her eyes was a fading Sora. She did not waste any time, sat up and ran towards the brunette, failing to notice Sora's Keyblade was on her right hand.
"Sora!" Kairi shouted but she came too late. Right at the moment she arrived at him, he vanished into pieces of light in the air. She also noticed Sora's Keyblade was in her right hand, when she looked at it, she heard Sora's voice in her mind.
"Take care of the worlds."
"Sora!" Donald yelled again. "Come back, Sora!"
Sora was falling through the darkness, slowly...
"What's... What's happening to me?" Sora quietly asked to himself.
"Falling... falling... into darkness."
After Sora's sacrifice, Kairi, Donald and Goofy were staring at the sky, in shock.
"Sora... Are you really- No. He can't be! I won't let him go!" Kairi said, grasping her necklace with her left hand. "But... Why do i have his Keyblade?" She questioned herself...
"Gawrsh, Kairi. Sora said to take care of ya and train ya, just like we did with him! Plus the King said to 'follow the key', so we're with ya now!" Goofy said, motivating Kairi as she smiled. "Thank you, Goofy." Kairi simply said.
"So, you have awakened at last, Princess Kairi." A powerful voice came out of a dark corridor. It was himself. Ansem, the Seeker of Darkness. However, he was not in Riku's body anymore, instead a new one.
The heartless symbol.
"A-Ansem..." Kairi was out of words. This was the man who destroyed their simple lifes and dragged her, Sora and Riku in this mess.
"The keyhole is now complete. Your job is now done. Now it's time to finish it-" Ansem was threatning Kairi until he saw her with that wretched kid's Keyblade. "No way..."
"BLAST THAT MEDDLESOME KID!" Ansem yelled loudly with Kairi, Donald and Goofy covering their ears. "Yeah, he gave me his keyblade. And he's NOT a kid anymore!" Kairi shouted back to him. She was clearly upset at this point.
"Doesn't matter. This is where it ends now." Ansem calmly said, trying to walk to Kairi, however, as soon as he tried to take a step, he was frozen. "What the..."
"NO! YOU.. W.. WON'T USE ME FOR THIS!" A sudden blast of light appeared, with a transparent Riku, who was struggling against Ansem's control. "KAIRI! YOU'VE... GOT TO RUN! THE HEARTLESS ARE COMING!" Riku shouted to Kairi, who nodded.
"O-okay... Not if you come with me!" Kairi called out to Riku, who shook his head. "Ansem has control of my body, and i can't hold it for much longer, so just RUN!"
"Can't you use the Heartless?" Donald asked the silverette as they begun to slowly walk away, who shook his head. "Any control of the Heartless i had is now in Ansem's." Eventually, Kairi, Donald and Goofy ran away, and Ansem dissapeared. the trio failed to notice that a single Shadow Heartless appeared on the place Sora sacrificed himself.
Kairi, Donald and Goofy were trying to run away back to the Gummi Ship, to regroup back at Traverse Town, slashing each Heartless that was on their way, still failing to notice that a Shadow was following them. It was until they reached near the Rising Falls that they noticed.
"Hey, look! a Heartless is followin' us!" Goofy exclaimed at the Heartless. Unlike most of them, which act on pure instict, did not attack any of them. It just stayed still, even when Donald bashed his staff at it.
"Confounded Heartless! Get lost, will ya?!" Donald shouted at it, but then Kairi noticed a light within the deepest darkness. 'Is that...' Kairi thought to herself, but decided to speak up.
"Sora? Is that really you?" Kairi questioned to the heartless, who just twitched his antenna. However, a wave of Heartless appeared, encircling her and Sora's Heartless. "This time, i'll protect you." Kairi said, summoning his Keyblade and putting in a battle stance. Due to trying to protect Sora, when many Heartless tried to attack her, she was horrified and summoned away her keyblade and hugged Sora's heartless.
"Sora!" Kairi called out to him when they were attacked. Donald and Goofy killed one when they noticed the horde attacking Kairi. "Kairi!" Goofy shouted, with the two animals with horrified faces.
However, a burst of light dissipated the Heartless away and miracuriously, Sora was revived, hugging Kairi. "Kairi, thank you."
When Kairi looked at the revived Sora, she smiled and quietly said. "Sora!"
"SORA!" Donald and Goofy shouted in unison, happy for him, as their last half-pint returned to the group safely. It was when Kairi noticed it, and summoned his keyblade. "Here. It's yours, isn't it?" Kairi questioned him. Sora slightly giggled and took his keyblade. However, another swarm appeared, and everyone took in their battle stances except Kairi, but then, the Beast suddenly appeared, roaring and killing heartless.
"GO! NOW! THE HEARTLESS ARE COMING!" Beast yelled at them, but Sora didn't like it. "Come with us!"
"No! I can't leave without Belle!" Beast shouted back at them. "Now go!"
The four of them ran away to the gummi ship to warp back to Traverse Town, to regroup after the madness.
AN: This oneshot was kinda in my mind for a while... So yeah, Kairi was able to use the Kingdom Key since she techincally got accidentally inherited the keyblade's power by Aqua... If I get enough support to make it running, then okay i'll do it.