You were the human who fell down Mount Ebott, just by accident. Waking up in a golden flower bed and staring up from where you've fallen down, it all started. The wrong things started to happen as a ghost spirit named "Chara" manipulated you into killing everyone down here. They possessed you, tormented you mentally and emotionally.

Soon, the moment came, where ut started to destroy you. They, Chara, killed everyone. At first, only some little monsters, but so on, they, with your possessed body, killed Papyrus, Undyne, Monster Kid, Mettaton, Muffet, and so on, until they stood before Sans.

The fights were brutal, and you suffered every time he killed you, until- there was a single chance for you to explain what happened, and after Sans saw that Chara again took over another human, he told you to reset for one last time, and avoid Chara on all matters.

-some days next-

After Sans freed you, out of pure empathy, he took you in. No one else bot him could remember what happened somehow. He remembered the resets, how many times he killed you and... has seen his younger brother Papyrus die a lot, but that's over now.

Right now, you're sleeping in Papyrus's room with him in bed because, sadly, the skeleton brothers' house has no spare rooms, but Papyrus was more than happy to have a human friend, after learning not to capture you.

"I, THE GREAT PAPYRUS, HAVE MADE THE BEST SPAGHETTI YOU WILL EVER TASTE! BUT DO NOT WORRY HUMAN, THERE IS ALWAYS MORE!"

Papyrus was mumbling in his sleep, something about having made the best spaghetti ever, and Sans used a magic spell to hide you from Undyne and Asgore. Today was the day Toriel would come again because she loves you a lot like her own child, and Alphys only comes to see if you have any sickness. Those two, along with MK, Grillby, and Mettaton, never told undyne or Asgore about you and couldn't remember what happened or the rest. Only Sans could.

[Note: you're scared of Undyne, Asgore still needs one human SOUL, only Sans knows the truth]