It all started in an Underfell timeline, the human had fallen and chose to do a genocide route. The human had already killed Toriel and made their way to Papyrus.
Papyrus: "Human! Prepare to meet your doom."
The human selected fight and struck Papyrus, lowering his HP by half.
Papyrus: "Hah! you think one measly hit can defeat me, you're going to have to do better than that, if you want to defeat me, the Great Papyrus!" Papyrus started his attack by sending a rather difficult-to-dodge bone-attack at the human.
The human dodged every single bone, and selected fight once more and finished off Papyrus. The human continued their journey and killed Undyne, Mettaton, Sans, and Asgore. After a reset was made, the human continued with another genocide route. They met Papyrus again and defeated him again, then moved on to killing every last monster over and over, reset after reset.
But after 20 resets something was off about Papyrus, he started noticing the resets like sans did. The Human approached Papyrus again but things were different this time.
Papyrus: "Human, instead of meeting your doom, how would you like to be friends instead, I mean I could easily defeat you, but I am feeling generous today."
The human stared at him for a moment, then selected fight and lowered his HP by half.
Papyrus: "Human, I am trying to be friendly with you!" Papyrus did not launch any attacks.
The human stood there for a moment, almost like they were thinking. The human then giggled and looked at Papyrus with an evil look. Papyrus noticed something off about them, they seemed almost like they were insane, or broken.
Papyrus: "Human, I know something is wrong, and I will accept your mercy if you spare me.
The human selected fight and finished off Papyrus, then continued killing all monsters again. Then another reset. The human had finished off Toriel and was making their way to Snowdin, but was stopped by Papyrus.
Papyrus: "Human, I am sure you are aware of who I am, but I would like to offer you a deal."
The human stood there silent.
Papyrus: "If you spare me now, I will not try to kill you, but instead I will let you go free, how does that sound?"
The human entered fight mode and selected fight then lowered Papyrus's HP by half again.
Papyrus: "GRR! Human stop your killing already!"
The human stopped their attack for a few seconds but then selected fight again and finished him off. Another reset was made after yet another genocide. Papyrus decided he would hide and follow the human, and watch for any disadvantages the human might have to use against them if needed.
As the human approached the last part of Snowdin, they noticed Papyrus was not around. They shrugged and continued, but Papyrus was a good distance away and followed them into Waterfall. Papyrus watched as the human killed Undyne, and then followed them to Hotland. He saw them kill Mettaton, then followed them to the Judgement Hall. There Papyrus watched in shock as the human attacked his brother right in front of him. As Sans limped away Papyrus jumped out from behind a column and caught him.
Papyrus: "S-Sans?"
Sans: "B-Boss, heh, sorry for bein' too w-weak..."
Sans turned to dust in Papyrus's arms.
Papyrus: "Brother... N-Noo!"
Papyrus got up and continued to follow the human, still shook up on seeing his brother die.
