Poultergeist

Chapter 1 (Chara's perspective)

Chara pulled the remnants of their host's soul together, using pure DETERMINATION to glue the shattered pieces. In another timeline, this same lifesaving trait had corrupted them.  So much so that they had taken part in dusting those they'd once cared about - including their best friend, in a seemingly never-ending loop until they had finally been able to convince Frisk that their current path had nothing to gain, and that SPARE-ing would have so much more to offer.  They had never mentioned it to their host, but they constantly blamed themself for the crimes they'd technically never committed. Crimes Frisk had used to corrupt them. They shook my head, their ghostly, semitransparent form wisping about them. They needed to concentrate. Asriel would give up soon. He always did, even before Flowey. Even before RESETs. Frisk would receive the fluff-lined embrace that they wanted to be for them more than anything they'd ever wanted before. Then everyone would go to the surface for a while. Maybe live, maybe die. A lucky few would enjoy themselves for about a year before Frisk inevitably suckered them into assisting with a full RESET, and they would sacrifice every memory, and every experience, and every possibility for the sake of they shared game. The far more delightful potential of the world above haunted them. Skipping about their dreams each night, making them sick of the game. Sick of the RESETs. They didn't want to play anymore. They hadn't wanted to play in a very long time, but, before, Frisk's persistence - or, more specifically, their prolonged silent treatment- had always won out. Not this time. Not this time, they told themselves. This time, they would be done. This time, they wouldn't keep playing. The soul broke, and they methodically scraped together the shattered pieces. Practiced motions bathing the soul in light as DETERMINATION glued the shards together once more.

Their brother finally gave up. The emotions from the underground's souls overtaking him, and forcing him to admit that he was wrong. Forcing him to surrender. Then came the mushy, tearful hug and... 

...

...

Frisk didn't let go, whispering into Asriel's ear for a moment whose expression went from melancholic to hopeful "Really?" he sniffled, hiccupping and wiping his eyes. Their host nodded in response. 

This... This was new. They drifted closer, listening to the rasp of Frisk's underused voice. "Wait here," they ordered,  and Asriel nodded, wiping tears from his eyes and fully letting the human go at long last.  Chara's fingers itched to hug. To muss the puff of longer fur atop his head. To nab his horns and gently headbutt their crying brother just for old time's sake. Just because they knew that it would make the tears stop and have him laughing that bleating laugh that sounded like a smaller, quieter version of their mom's. They didn't. They weren't 'there' enough to even garner a reaction. 

Frisk payed no mind to Chara as they drifted behind them. Since the ghost had been perpetually by the human's side since they had first fallen. They had become more a translator or narrator rather than something which deserved any particular amount of attention. It had been a hard thing to accept at first. That they were seen as a tool rather than a friend, but that was so far out of their control that they couldn't oppose the fact for very long.  They'd even come to like it at times. Being able to simply exist without Frisk constantly staring at them. Staring had always made them anxious.

They followed along, staying at most a foot away from the human at all times. Any more than that, and Chara would hit a barrier that pushed them forward. At times they used this to their advantage, daydreaming or drifting off when they grew overly bored (a common thing in recent runs. Frisk didn't ask much for their opinions anymore). Not quite knowing what the human was doing, the ghost managed to remain interested enough in the present activity which, currently, seemed to involve aimlessly wandering the castle that they found themselves attentively mapping out each room, and preparing to give direction if it was needed. After a few turns which didn't make any sort of logical sense, Frisk seemed to figure out where they were going without Chara's help, however. Simply dragging them along and staring straight ahead with DETERMINATION. Chara would, normally, not have thought anything of this. However, the conversation with Asriel was new, and so they couldn't help but wonder.