I never defeated Sephiroth in KH1, but I hear it's plausible or something.
O.H.A.N.A.
Chapter One: In which the planet Ee-arth welcomes a visitor from the stars
Sephiroth was quite certain that there were worse things that could happen other than being bested in the Coliseum by a key-wielding fourteen-year-old boy.
He had yet to think of one, but he was working on it. There was no hurry. He was floating through the weightless, empty space that lay between worlds, his body curled up like a child in a womb, his one wing pulled over his head. He was protecting something resting inside a burlap sack, his long hands carefully holding the bundle to his stomach.
There was no air and he had to concentrate so he wouldn't suffocate. His head was clouded and felt like there was barely anything inside it. Every now and then he would be shaken from his half-sleep by a sharp bump that throbbed over his skull. His eyelids fluttered and he saw something wet and red clustering in the space around him.
Sephiroth never slept. It just wasn't something he did. He was a god, or the son of one just like the hero of the Coliseum, at the very least. He never got tired or hungry. Then again, he had never been defeated, either. When he thought about it, he had realized a lot of new things that day. For one thing, when a sharp, metal object like, say, a criminally oversized key, was, hypothetically speaking, thrust into his side, his clothes wouldn't split, but the skin over his ribs would bruise like they had been hiding behind tissue paper instead of leather. He knew he wasn't human, but that didn't stop the heartless from swarming around him, either. Usually he was protected, by Her, but that match in the Coliseum had been disappointing and the Masamune could only wreak so much death and destruction at once before even he, after a day and a half of cutting and summoning all sorts of gory fire and brimstone, reached a limit. Apparently even he had his bad days, too. He did actually have blood under his skin. He also breathed air just like everybody else, when there was air to breathe.
Sephiroth floated for a long time, utterly helpless with no gravity to keep him grounded and no air to support his one, battered wing. Aside from the burlap sack and his faithful, bloody sword, he had absolutely nothing, until he got caught in the orbit of another world.
If Sephiroth had realized what was happening at the time, there was very little he could have done about it anyway other than maybe say a prayer to his mother because no one can hear you scream in space. Not that Sephiroth ever screamed, either. That, unlike the other list of things Sephiroth never did, existed in a dimension on the other side of the forth wall all by itself.
Gravity is a very useful thing, but for a Gummi Ship-less space traveler, there are mixed feelings, a love and hate relationship. You'd love to stop floating in the endless abyss, but when you finally hit the ground, you were going to hate it.
Sephiroth eventually felt gravity pulling on him. His body was suddenly all too heavy and his skin and clothes were on fire. He closed his eyes against the blinding light and kept the parcel close as he concentrated.
Millions of steadily shortening miles below on the unfortunate planet, a girl sat in her room with a bucket of black paint in front of a canvas. She was thinking very deeply about the piece she had painted on the paper and had one grubby hand stroking her round chin. She was an extremely observant child, so when her wandering gaze eventually found the window, she couldn't help but notice the large ball of flames breaking atmosphere.
"A shooting star!" she yelled, running to the chipped wooden windowsill. "Quick, Stitch, we've got to make a wish!"
The girl got down on her knees and clasped her hands together, bowing her head and drawing her eyebrows seriously in thought. Behind her, an ominous noise grunted from under the bed, and a furry blue something crept out from under it. The ugliest dog known to man took one look at Lilo and rolled his eyes, making a face and an unimpressed blah noise in his throat. His large ears twitched as he recognized the whistling noise the girl couldn't hear. He made a point of stepping through a spilled puddle of paint and trailing dark footprints over the floor as he padded over to the window. Stitch looked outside, curious, and his eyes narrowed as he watched the flaming meteor make its way to their island.
It hit the ground and the world went white, a loud crack and a boom sweeping through the trees and making the old wooden house groan. Lilo was thrown off the floor with a screech and landed all the way across the room, on top her bed, the pictures on her wall flapping frantically against the tape. It was all over in a second and she blinked, rubbing her eyes to get the spots out of her vision. The first thing she saw was Stitch looking over the mattress at her.
"Happy birthday," he said sarcastically.
Lilo climbed down and ran to the window, practically falling outside as she searched the dark horizon. The sun was just beginning to rise from behind the horizon and a yellow glow was illuminating the conspicuous pillar of smoke curling up between a cluster of palm trees.
"Wow," she said quietly.
If Stitch had any opinion on the matter, he didn't voice it. Lilo turned around to find him busily putting footprints all over her walls.
"Hey, stop ruining my wallpaper," Lilo ordered, sticking her hand out and pointing at the floor. "Come on."
Stitch growled at her but dropped to the floor and wiped his paws on the towel she gave him. While Stitch was busy tearing a hole in the towel and snarling, Lilo grabbed her bag, which nowadays was always packed and ready to go, put her sandals on and flip-flopped her way out of the house. Stitch swallowed the piece of towel he'd been gnawing on, slung his ukulele over his back and crawled out the window to meet her on the porch.
"Day twenty-seven," Lilo began, looking both ways before they crossed the deserted street and headed into the jungle. "Another unidentified object fell from the sky, scorching in flames before it fell near our house with an explosion that killed trees, houses, and a whole lot of wild animals. It struck fear into the hearts of everyone who saw it and sent people screaming into the streets. Everywhere we looked there was maddening chaos. Despite these perils, our team unanimously voted to search for the crashing site and whatever there is to find."
Lilo paused. Dead silence met her ears. The streets had been empty for days. Nearly a month ago, all those black creatures started showing up, and grownups started disappearing. She gave Stitch a serious glance and grimly faced the deep jungle ahead, dropping her sunglasses over her nose.
"As always, we are prepared for the worst."
TO BE CONTINUED