If you start a genocide/kill everything run, Papyrus begs you to give up, and spares you. Because he has such unyielding faith in the goodness of people. If you spare him he'said happy you "didn't do a violence" and decides to become your friend.
Frisk sat in the corner of the fairly empty shed. All that was in here was a dog bed, a bowl with kibble and a cut up water sausage, and a chew toy. They wondered if the skeleton brothers owned a dog. They wrapped the worn blanket they were given tighter around them... not to shield from The cold, but something deeper. Perhaps fear? They didn't know what was going to happen next.
They were startled from their thoughts by the door opening. Both skeletons entered. The shorter one stayed by the door, glaring at Frisk untrustingly. The tall one, who called himself "the Great Papyrus " approached the bars blocking the door. They were easily too wide to effectively keep them in. But thoughts of running away, escaping never accured.
"GREETINGS HUMAN! I WAS WONDERING IF PERHAPS YOU WERE HUNGRY, SO I THE GREAT PAPYRUS HAVE BROUGHT YOU A PLATE OF FRESHLY MADE SPAGHETTI! "
Papyrus layed the plate of pasta at Frisk's feet. They couldn't take it. Tears started pouring from their eyes. "Why!?" Was all they could get out before sobbing.
Papyrus looked confused. "WELL I BELEIVE HUMANS NEED TO EAT A LOT, AND IT ACCURED TO ME THAT PERHAPS DOG FOOD WOULDNT BE SUBSTANTIAL ENOUGH. SO I DECIDED TO MAKE YOU A PLATE OF MY SIGNATURE SPAGHETTI! "
Frisk looked up, sadness and frustration clear on their face. "No! Why are you being so nice to me! I killed so many people here, I don't deserve your kindness! Why? I just don't understand. " They covered their head with the blanket.
Papyrus looked over to his brother, who just frowned at the human. Papyrus didn't really know what to say, so he let his instincts guide him. He layed a gloved hand on their head.
"HUMAN, EVERYONE MAKES MISTAKES! THE IMPORTANT PART IS THAT YOU REALIZED YOUR MISTAKES BEFORE IT WAS TOO LATE. WE CANNOT CHANGE WHAT YOU UHAVE /U DONE. BUT WE CAN CHANGE WHAT YOU UWILL /U .DOES THAT MAKE SENSE?"
Frisk rubbed at their eye and thought about it. Thought about everything. That flower had told them that they were supposed to kill everything or everything would try to kill them. Even the goat woman tried to do that. But this tall skeleton showed them kindness... was the flower wrong?
"I guess. I'm sorry. For every thing. I was confused I guess?"
"THAT IS UNDERSTANDABLE. I'M GLAD YOU HAVE DECIDED TO CHANGE YOUR WAYS. PERHAPS NOW YOU ARE READY TO EAT SOMETHING?"
Frisk stomach growled. They did feel hungry now. They brought the plate of pasta closer. They put a fork full into their mouth, their face reflexively scrunching. The taste definitely was indescribable. Looking up at Papyrus they noticed a look of waiting anticipation. Was he waiting to see what they thought? After the kindness they showed, they didn't feel right to insult his cooking. All they could muster was a thumbs up. They were rewarded with a smile from the skeleton.
"I'M GLAD YOU LIKE IT. EAT UP, HUMAN. YOU SHOULD BUILD UP YOUR STRENGTH! IN THE MEANTIME I SHOULD CALL UNDYNE, AND UPDATE HER!" Papyrus left the shed, his brother staying behind.
"Thanks for being nice to my brother."
He left at that. Frisk shrugged and finished their pasta. For the rest of their journey, they tried hard not to attack, tried befriending monsters instead. It was hard, but they persevered.