I wrote this story a while ago, and I'm finally crossposting it here. This one is meant to express my headcanon about Chara and their psyche. I hope you'll like it. Also, this story has two alternate endings!
Disclaimer: I don't own "Undertale", it belongs to Toby Fox.
After monsters and their new human friend Frisk left to the Surface, unbenknownst to them, a faint red glowing figure materialized itself in the Underground, in the very last room before the exit. It was Chara, the first fallen human. They looked around them, surprised by this outcome of things, then at their own hands, getting used to having limbs again (sort of). Confusion quickly got replaced by realization. Chara was no longer linked to Frisk, they were no longer in the limbo sleep their spirit's been for many years. As they searched through their memory, Chara understood what happened.
After they and Asriel died, their Soul couldn't cross over (likely because of their unfinished business) and it faded away, leaving Chara's spirit hanging in limbo for many years... They were pretty much deeply "asleep", until their sleep got disturbed by Frisk's arrival in the Underground. Frisk, unbeknownst to her, had absorbed some of Chara's determination from the golden flowers, thus absorbing some of Chara's mind. Of course, it wasn't enough to fully awake Chara from their comatose slumber. They still were mostly dormant throughout Frisk's journey, but they could get bits and pieces from what Frisk saw and experienced. Chara couldn't wake up and interact with the world, but they could sometimes resonate just enough to give Frisk some glimpses of their old memories, or a very strong intuition. But by the end of Frisk's journey, her body had produced her own DT, naturally renewing it, which eventually cut off Chara's link to Frisk and freed them, allowing the fallen child to wake up in the form of a ghostly spirit.
But soon enough, Chara realized this wasn't exactly freedom. As they explored around, both in the Undergound and a little on the Surface, Chara couldn't interact with anyone or anything, because they still were invisible and intangible. All they could do was to fly around, unable to talk to anyone.
Well, almost. Several days after their reawakening, Chara came across Flowey. To their big shock and surprise, the latter saw them! It made sense, considering Flowey was a revenant. The siblings' reunion was an odd mix of emotional and awkward, for multiple reasons. But at least, Chara no longer was as lonely.
And yet... Being a ghost was only a part of Chara's problem. After they fully awoke from their limbo sleep, Chara could remember things from Frisk's journey. Since their DT has been in Frisk's organism, it gave Chara access to some of her memories. And most of what they saw... was painful. The first time Chara fully processed those memories, they wished they never woke up, because their old family wasn't the one they thought they knew anymore. "They all just forgot about me..."
Chara no longer knew for how long they've been around. Was it weeks? Months? Either way, they didn't care. Time was meaningless for a ghost like them. They were again sitting alone in the former Barrier room, looking through the exit door, gazing at the sunset with disinterest. Nothing could bring some joy or excitement into them anymore, Chara realized. Not even the fact their (former) family was fully happy on the Surface. How long would it take until they surrendered to insanity? But before Chara could ponder on the matter any longer, all of sudden, Flowey popped up from under the ground and looked at them with his usual, albeit more genuine this time, smiling expression. Flowey spoke up with a calm and cheery voice, or at least, what supposed to sound like it.
"Hi. Seems as if everyone is perfectly happy. Monsters have returned to the surface. Peace and prosperity will rule across the land. Take a deep breath. There's nothing left to worry about."
Flowey's tone grew somewhat nervous at his latter sentances. He then looked into his best friend's reddish eyes and spoke up with hesitation.
"Well. There is one thing. One last threat. One being with the power to erase EVERYTHING... Everything everyone's worked so hard for."
Chara didn't say anything and gave the flower a knowing look.
"You know who I'm talking about, don't you? That's right. I'm talking about YOU." - Flowey said seriously - "YOU still have the power to reset everything. Toriel, Sans, Asgore, Alphys, Papyrus, Undyne... If you so choose... Everyone will be ripped from this timeline... and sent back before all of this ever happened. Nobody will remember anything. You'll be able to do whatever you want."
"So, if I just reset everything... I could start it all over again... or do a completely different path?" - Chara realized with wonder. The idea was admittedly very tempting. It would be much better than being stuck there in the dark forever, with no one but Flowey for company, right? "All it takes is to really want it... Now I know for sure I too have access to that power..." Even without Chara saying anything, Flowey could guess what they were thinking about. He's been their best friend for a long time in the past, so he got to know their mindset pretty well.
"That power. I know that power." - he stated, his look just as serious - "That's the power you were fighting to stop, wasn't it? The power that I wanted to use."
"I wasn't really fighting it, honestly." - Chara muttered - "It's a neat power."
"You must be confusing me with her again." - they then thought to themselves, not without some bitterness. Flowey ignored Chara's words and went on, with a now sadder expression. Or at least, he looked as sad as his soulless condition allowed him to.
"But now, the idea of resetting everything... I... I don't think I could do it all again. Not after that."
Was he even as soulless as he claimed? Not that it really mattered. What mattered more was what he just said. "So, she really impacted you that much, huh? Even though you barely know her." - Chara mused, but didn't say this aloud.
"So, please. Just let them go. Let Frisk be happy. Let Frisk live her life." - Flowey pleaded, and he sounded more genuine than ever in his flower life.
"Just let go? Let her be happy while I'm stuck here?" - Chara inwardly screamed - "So her happiness matters more to you than mine?!" Chara wanted to sob at that moment, feeling overwhelmed with anger and loneliness. Flowey, their so-called "best friend" tells them they still have some scrap of control over their fate, only to beg them to give up on it?! Was that some bad joke?! Chara was silent, but Flowey could sense how resilient they were to just give up on that power. He could see it by how Chara was clenching their fists, and how the glow of their ghostly form frantically dimmed or brightened, their eyes now crimson red.
"But. If I can't change your mind. If you DO end up erasing everything... You have to erase my memories, too." - Flowey then warned, hoping to add in another factor.
This made Chara perk up just a little. If Flowey lost his memories of this big journey... it meant he'd revert to his old evil ways, and the tiny piece of Asriel within him would be lost again. This made Chara want to reconsider. But before they could ponder on this or say anything, Flowey spoke up awkwardly.
"I'm sorry. You've probably heard this a hundred times already, haven't you...?"
"Um, no? It's the first time I hear you say that." - Chara replied, their expression mildly dumbfounded.
They could see a shadow of relief in Flowey's eyes at that. "Wait. He thinks this might've already happened, since he has no way of knowing..." - the ghost child then mused - "So what he said about erasing memories is true."
"Well, that's all." - Flowey said with a small sigh, not knowing how else to end this awkward talk - "See you later... Chara."
With those words, he went away, leaving Chara by themselves again. This didn't really bother Chara, since their conversations never lasted for very long. But now, they had a different matter on their hands. Chara now had the confirmation that they too had access to the Reset power. Was it due to their determination, their will to live? Or was it due to the connection they once shared with Frisk? This idea kinda repulsed them. "Linked to the girl who took from me everything I had... How pathetic." It really was. Without Frisk, Chara wouldn't even have this dilemma now. Heck, they wouldn't even be there in the first place! Even though it was good to wake up from the void-coma, it wasn't as great to be stuck as some earthbound spirit, and an incomplete one, that is. Even after Chara "reformed" in their new ghostly form, they still lacked their Soul. Maybe this was why they felt so miserable and empty inside? Perhaps. "Even if I still had my Soul... it wouldn't change anything. It wouldn't change what they did." - Chara thought bitterly. "Toriel replaced me without a second though by a new human kid..." - angry tears flew down their ghostly flushed cheeks - "Did she ever truly care for me, or was I just a pet of a sort, to be replaced by another one at my death?" Toriel's had six other human children before Frisk. Whenever one died, Toriel moved on and replaced them by a new one. But she wasn't the only faulty person here. Asgore wasn't any better. Instead of giving them a proper burrial, he had intended to keep Chara's body in some coffin in his basement... If that wasn't messed up or creepy, then what was? So much for being "the hope of humans and monsters"... "It's no wonder he forgot about me, I wasn't his child, but a peacemaker for his kingdom." - Chara's tears turned black and thicker - "He didn't even care to remember me! "I just want to see my wife, I just want to see my child", he said. "Child", not "children"?! And what about me?" Chara's ghostly form was turning a darker shade of red, and the black substance leaking from their eyes got a lot thicker. In his last moments, Asgore had no thoughts for them! But of course, Asriel got that privilege. Asriel... The friend who betrayed them, who couldn't go through their perfect plan. And if this wasn't enough... "I wasn't the greatest person, he says? Well then, I won't even try to be. He prefers Frisk over me anyway..." Chara's eyes were now fully dark, so much that their red irises were now invisible.
"They must pay for this! I'll... I'll make them pay..!"
As those words were spoken, Chara was filled with determination like never before. All they needed to do was to aim it all towards their goal; eradication of the enemy. Chara couldn't do it in their current form, they needed Frisk's body to do that. That's why resetting the timeline was their best chance. "All I must do is to reach the power and command it to reset..." Closing their leaking gooey eyes, they concentrated and felt like they connected to something really powerful... It was almost as though they were touching it. In just a moment, this timeline would be no more...
But then, Chara paused. Should they really use this power? They felt conflicted. On one hand, they were really angry at everyone for having forgotten them, but on another hand, Asriel was still their brother and monsters were their family. Chara wanted get revenge, to make monsters feel their pain, but they also felt reluctant at taking away the happiness everyone finally found.
"Why am I making this so difficult for myself?!" - Chara grabbed their hair in frustration - "I must decide, now!"
They had to make a choice and accept its consequences. Reset and get the satisfaction that their "family" paid for the wrongdoings, or just let go and let them be happy... while possibly spending the eternity as a miserable spirit? It was Chara's family's happiness, or their own satisfaction. After a long minute of thinking, Chara finally decided.
RESET
Chara smiled widely, creepily even. And just like that, they unleashed that mystical power, rewinding the timeline. Feeling the world reset around them, Chara let out a loud and uncontrolled laughter, one full of satisfaction and anticipation. At that moment, something changed at the very core of Chara's phantomatic being. Giving in their own anger and rancor corrupted the passive ghost into a vengeful spirit.
...
With a gasp, Frisk opened her eyes, finding herself lying on a bed of golden flowers. High above her, she could see sunlight coming through a hole. She realized she just fell through that hole, right under the mountain. She also had a vague feeling having seen a dream just now, but she couldn't remember any of it. Sitting up, Frisk mused: "The flowers must've cushioned my fall..." Then, she felt like an odd sense of déjà vu. It sent a shiver down her spine. How could this possibly feel familiar in any way? She never got herself in this kind of situation before! Standing up shakily, Frisk stepped off the flowers and frantically looked around her. She fell underground, now she had to find a way out.
"H-Hello..?" - she called out - "Is anyone there? Anybody?"
Frisk got taken over by tremors. She felt cold inside. Yes, falling underground was a bad situation enough, but... something else was just giving her the creeps. There was just some unpleasant feeling, as though something was off. "I'm not supposed to be here..." - Frisk thought as she walked towards a big ancient door - "Where else would I be though? I fell because I was foolish enough to climb the mountain." And yet, despite her reasonable thoughts, Frisk couldn't chase away the invading sickly feeling.
Little did she know that what awaited her was a path traced with monster dust. Dust that resulted from her violence, her kills, which in turn were fueled by that same unpleasant feeling. Everything felt wrong about this place, about the monsters she met... even about herself.
"Kill..." - something in her head was telling her, over and over.
The cold and sickly feeling only grew very quickly, until very soon, Frisk diddn't feel anything. It was as though her body wasn't even hers anymore.
And in fact, it no longer was.
When she stood in front of the mirror in Toriel's house, she could only vaguely register that her reflection looked back at her with red eyes. "Shouldn't my eyes be brown..?" But there were no further thoughts on the matter.
As her mouth curved up in a creepy smile out of her control, a voice that wasn't hers whispered:
"It's me, Chara."
The once fallen child was back.
Let them go
Chara let out a sigh and shook their head. "No. I'm still very mad at them for replacing me, but taking away their long awaited happy ending wouldn't be right." And just like that, Chara gave up on their chance at revenge. Reluctantly, yes. Nonetheless, they felt an odd sort of inner satisfaction. Doing the right thing felt... good.
Once the choice to let them all go was made, something surprising and incredible happened. In the darkness of the former Barrier room, some bright light shone from somewhere above, unlike any day light that could be seen through the hole above. A light that was unnaturally white. About at the same time, Chara felt a familiar warmth where their chest was, and when they looked down, they briefly saw a red heart glow there. "My Soul..?" - they thought with a gasp. Curious, Chara floated just a little closer to the light. They squinted their eyes, which widened the next moment, when they saw a figure come out of the light. It was a human looking woman, wearing a simple long white dress, emitting a white with hints of purple glow. She had blue eyes and her brown hair was styled in a pixie haircut. From the woman's back, a pair of glowing white wings could be seen. Those weren't like bird wings, they were morre reminiscent of the wings on the Delta Rune symbol. Chara looked at her in awe for a moment, then asked bluntly:
"Who are you?"
"I think you can already tell, Chara."
"An angel..." - Chara breathed out - "But why are you here?"
"You let go of what bound you to the realm of the living. Now, you are free to cross over to a much better place."
"So you're here to guide me... up there?" - Chara asked, awkwardly pointing up.
The angel nodded with a kind, yet slightly amused smile. Chara then looked behind them, in the direction of the door that led to the surface. Their eyes glittered with unshed tears.
"That means... I'm really... leaving them now."
"You'll still be able to watch over them." - the angel stepped towards Chara, resting a gentle comforting hand on their shoulder.
Chara flinched just a little at the touch. The angel judged best to tell Chara some more about herself, to establish a start of trust.
"I know what you've been through, Chara. I know because I've been watching my daughter go through the Underground."
"Wait, so you're Frisk's mom?" - Chara frowned - "That's why you're the one to come for me."
"My Frisk is happy and has a good family now. You have no one. Nobody should be left out alone, whether they're dead or alive."
"Whatever... I don't need your pity, angel." - Chara muttered, looking away.
"That's not pity, but genuine compassion." - Frisk's late mother offered her hand - "Come with me, Chara. You won't suffer from bad memories or be alone anymore."
There was a moment of silence. Chara, being naturally wary, looked into the angel's eyes as though seeking for a trick, but the latter's eyes reflected nothing but purity. Then, Chara realized they didn't want to be miserable in the world of living anymore. Their time there was over, and even before that, their life hadn't been the best. But it hadn't been the worst either, thanks to all the good times they've spent with the Dreemurrs. Their family has moved on, and it was time for Chara to do the same. They slowly reached their hand, then after a brief pause, grasped the angel's one.
With a tender smile, the angel led Chara into the light.
A/N: Frisk's mother watching over Frisk throughout her journey is a favourite headcanon of mine. Like in my OUAH series, I usually imagine Frisk climbing the mountain because of the stories her mother used to tell her.