Wolfwalker2
Basically, a genocide run happens, and Frisk agrees to ERASE the timeline, but Chara says that first, they will need Frisk's SOUL. Frisk gives away their SOUL, and in the moment that both of them are touching the SOUL, they are RESET by an outside power.
The RESET gets both Frisk and Chara's personalities and spirits sucked into one SOUL, and create a new person with a determination SOUL. Their name is Kaia (decided by Frisk and Chara .
Kaia, unlike Frisk and Chara, has no backstory, and lives in a glitch of the main timeline, where Chara gives away their SOUL while dying from cancer, and the monsters are freed by using Chara's SOUL along with the other fallen humans. That's why Flowey doesn't exist.
Frisk never falls down into the underground, and Kaia falls into a world where they don't have accesses to the RESET button, and an underground where everybody there is insecure about going to the surface. Guided by Frisk and Chara, they have to chose one path to follow. Pacifist or Genocide.
Frisk is pacifist, trying to RESET without harming anyone while Chara is willing to kill anyone to get back to normal. Both Frisk and Chara want to RESET so their glitch world disappears, and has to find the RESET button to do that.
All of the characters are the same as normal except Asriel, because Flowey never existed, Chara and Frisk, because they only exist along with Kaia as a glitch from the main timeline.
Then there are two timelines (there's still a neutral timeline, but you don't get the RESET button. Also one timeline only could coexsist with the other because of the multiverse theory, but if the multiverse theory isn't true, then they wont be able to happen. So there's no Ink!Kaia, or Outer!Kaia, unless you really want it to happen, just ask me for permits, and give me credit if I say yes).
TW: There may be some blood, but I don't plan on it.