Mmm, this one is kind of...over the top, excessively dark, excessively angsty, and so on. It certainly at least tries to take the dark tone Dream Drop Distance has at times, which was intended, but... I know this isn't everyone's thing, and I'm sorry. If you're not into this sort of thing, which is completely understandable, please turn back.
This is based off of an Undertale/Kingdom Hearts AU my friend and I have been working on for awhile now. However, it's just based off of it, I currently don't consider it canon. And I don't think it WILL be, either. If things change, then yeah, I'll change this accordingly, but this is probably going to be how things are.
This particular story is based off of the end of Sora's story in Dream Drop Distance. The main roles in the Underheart AU you need to know are as follows: Frisk serves as a sort of Sora, Chara serves as a sort of Xehanort, Xemnas, and maybe some other variations, and Asriel is a sort of combination of the roles of Kairi and Riku.
Chara here is based more off how they come off in the Genocide run than how I'd think they were when they were alive. Their main concern is power.
There was an impact, and Frisk felt solid ground beneath their feet. Their eyes flew open. They knew where they were, but they had no idea how they'd gotten there. Nor did they know why they were here. They didn't want to dwell on their uncertainty, since no answer they could imagine would be any comfort.
Around the was a limitless expanse of darkness. They could just make out the ground below them, but that was all. There was no exit in sight, no entrance, just an area filled with nothing but darkness. It was quiet, too, almost maddeningly so. They knew this place, they'd been here before. And they hadn't wanted to come back again. This was the end of everything. The absolute.
It had started out as just a test. To thwart the plans of the other humans (and specifically, their leader), Frisk and Asriel underwent the the Mark of Mastery exam. If they could prove themselves as keyblade masters, then they stood a chance at claiming victory in the inevitable final battle. In order to undergo this exam, the timeline had been reset. Frisk and Asriel were to eliminate any threats to the timeline and gain a new power they would need to be victorious. Meanwhile, all their companions remained in an area where time was more flexible, safe from the effects of resets. There, they would wait until the exam was complete, and whether the two had passed or not would be determined.
But things had gone south pretty fast. The humans seemed to know what was going on before the exam even started. They started interfering almost immediately, directing the exam down a different path than expected. Not only that, but Frisk and Asriel had thought they'd be working together during this exam. However, they'd been separated from the start, and Frisk wasn't sure anymore whether they were supposed to be, or if it was the humans' interference. But it didn't matter now. One way or another, they had reached the end. But this wasn't the end they'd intended.
They had reached the end, but they hadn't gotten their alone. In front of Frisk now was another human. Not just any human, either, but the human who had been in the Underground the longest, who lead all of the others. Frisk knew now that their name was Chara. Frisk also knew that they had no good intentions for the Underground. In a way, they were still following the exam, they supposed. The humans were a big threat to the timeline. Frisk still had a chance to pass.
But that wasn't even their biggest concern anymore. Chara had followed them a long ways through the Underground, for most of this timeline. They were the one who lead Frisk here, where Frisk had once fought their best friend, the end of it all. Chara had directed them through most of this timeline, unbeknownst to Frisk. And Chara was one of the most dangerous humans of them all. If Frisk could get back to everyone else safe, they would be lucky.
The two stood in silence for some time, Frisk trying to figure out what to do and Chara seeming to be planning their next move carefully. Finally, it was Chara who broke the silence.
"We've reached the end," they mused. "The absolute."
Frisk said nothing.
"Getting this far was no easy task. But I have you to thank for our success. We may have guided you here, but if it weren't for your determination, we wouldn't have made it. Neither of us would be here now."
Frisk said nothing.
"That's the problem with humans, you see. We're determined to a fault. It's lead you straight into our hands, exactly where you didn't want to go. And now you're in too deep. Not even your best friend can save you now."
Frisk scowled.
"It makes me glad I'm rid of mine," Chara continued. "With no soul to get in my way-"
"Then why are you doing this?" They would've went on, but Frisk uncharacteristically interrupted their explanation. They rarely said much to anyone, but frustration they barely realized they'd had was boiling over. If Chara was happy without a soul, what was the point of all of this? All the fighting, turning friends against each other, striking against the one human down there who still had their soul, a soul both humans here claimed to desire. Since Frisk had met them, everything Chara had done was in the name of gathering human souls... "If you're so happy without a soul, why do you keep looking for them? Why do you keep coming...after me?"
Chara laughed. "Really, Frisk? I thought you were smarter than that. Don't you remember anything you learned down here? Don't you remember how powerful human souls are?"
Of course they did. But what was Chara getting at? They kept switching positions, from despising human souls to doing anything to get one. Frisk couldn't see whatever Chara was getting at. They fell back into silence.
"What I said about souls is true. All that determination can lead you astray from what you desire. They're disgusting, too, made of nothing but greed, hate, and desire to cause suffering. But they have their perks, too. Especially yours, Frisk."
Frisk swallowed. "My determination..."
"Yes." Chara smiled. "Resetting. The ultimate power. But that's not all I want from it, either. That's just a happy bonus."
"Then what is it you want?!" Frisk demanded.
"Isn't it obvious?" Chara laughed again, louder and more menacing than before. Frisk subconsciously took a step backwards. "Your soul is the last piece of the puzzle. Did you really think the Organization's true goal was to reclaim our lost souls? I have no desire for useless emotions, and I would never give the other humans something so powerful. That false goal was just a means to gain allies."
"Then you...you were going to..." The gears in Frisk's mind were turning. They were arriving at the answer just as Chara was getting to it.
"Exactly. Once I found you, I had everything I needed. The true goal of the Organization of Eight was to obtain seven human souls. We know where six are, and we only need yours. Once I have them, I'll find a way to absorb them. Whatever those scientists say, I will find a way. And once they're mine, I will become the god of this pathetic world."
"You can't...there's no way." Frisk shook their head. "And even if you could, I won't let you. You can't have my soul."
"I didn't ask for permission," Chara state calmly. "But regardless, your words mean nothing. You only made it this far because I guided you, I allowed you. It's pointless to try to stop me."
Frisk held out their arm to the side, saying no more. A keyblade formed in their hand, one they'd never seen before. It was a long, thick weapon that was devoid of most color. The hilt was heart-shaped, like many of their other keyblades, but the shape of this one was more rough and jagged. Long, deep grooves covered the entire thing, with bandages crafted over many of them. Its teeth took the shape of half a save point, made the same gray color the rest of the blade was, and only one end stick out. The keychain was a black heart. This keyblade was unfamiliar to them, and they were unsure even of its name. However, if this was the keyblade that came to them, this was the one they would use.
"Your determination will lead to your own demise. But it doesn't matter. The end result will be the same.
With a grin, Chara summoned a keyblade of their own. Far from elegant, this keyblade was even more crude than Frisk's. The hilt was shaped like a yellow save point, with just enough space in the middle for a grip to hold on to. The short blade looked simply like a red knife, with no teeth whatsoever. The keychain was half of a red heart, jagged and sharp on the ends. It was a terrible thing with no sense of beauty, but Frisk supposed Chara didn't care for that. They just wanted to get the job done.
It was down to this. If Chara got the souls, there was no telling what they would do to the timeline. This stopped being about a simple exam long ago. Frisk had to end it here and now. For the Underground. For the timeline. For their friends.
Chara ran forward, swinging the blade down from above their head. Frisk rose their own just in time to block the hit.
How long did it last? Did they win? Did they lose? Frisk wasn't sure. Everything seemed eternal in the black nothingness.
They couldn't see Chara anymore. The world was quiet and dark. Exhausted, they collapsed to the ground. The fight had taken everything they had. They had no strength left. They prayed it was really over. Everything seemed eternal in the black nothingness.
Frisk closed their eyes for a moment. When they opened them again, Chara was standing above them, smiling. The quiet around them continued, broken only by the occasional sound of Chara's voice.
"I told you, you can't defeat me. And now, your determination has become your downfall."
The silence around them was deafening. The darkness that surrounded them was blinding. Everything seemed eternal in the black nothingness.
"Seven human souls. With that kind of power, I will have complete control over everything. And thanks to you, I have them all."
Frisk blinked slowly. Everything disappeared from view. And then they saw Chara once more. Frisk's vision began to blur. Chara melded in and out of the darkness. They couldn't let this happen. They couldn't let Chara win. They would not let this happen.
Closing their eyes again, they attempted to reset as a last resort. There was still a chance if they could go back. They could prevent this. But their determination was weak, their strength completely sapped. When they opened their eyes, nothing had changed. Time hadn't reversed.
"Oh? Your strength has been reduced to nothing, and yet you still don't give up."
The silence was deafening.
"You seem to have misunderstood. Not even a reset can save you now."
The darkness was blinding.
"You cannot fight back, and there's no one here to help you. You've failed."
Everything seemed eternal in the black nothingness.
"Your soul and your determination are now mine. And you'll be left as I was: an empty, soulless vessel. You'll have nothing, and I will become the god of the only world that ever offered me happiness. So hold on to your despair. Hold on while you still have something to feel."
Everything seemed...
Chara smirked as Frisk closed their eyes once more.
Normally I would try to write a Chara fight, and this would be a lot longer. However, there's a lot of great fan-made Chara fights out there, and I wouldn't want to accidentally take from those. I don't have any good ideas anyway, so I wouldn't be able to come up with any by myself. That's a task for another day.
I'm so, so, so, so, so sorry.