Click.
He unlocked and opened the door with fire seemingly escaping from the crack between the it and the olive carpet.
It creaked open due to the door not being used much since his brother gained his teleporting ability, and Papyrus made a note to fix that once it was all over.
Once he stepped inside, the door slowly closed behind him. He scanned the room, looking for anything that might help him. He saw the ball of sheets, the trash-nado, and the sock pile. But something from the drawer caught his attention.
He picked up the item, pro in itself to be a brass key with the words "behind house" scratched into it.
Going to the location on the key, Papyrus opened the front door as a mixture of snow and dust blew against his skull. He walked around the house, surprised to see a narrow passageway behind his shelter.
He opened an almost new door, which lead to a staircase that seemed to go forever.
He descended down the staircase, seeing pictures of Sans with many people he didn't recognize. Some of them, he swore he saw before, but he just couldn't but his finger on it.
Dust and cobwebs were collecting on the walls of the stairway, meaning that he was one of the only people to walk down here.
After what seemed to be 5 minutes of strange pictures and dusty walls, he reached another door. Papyrus opened said door, and the first thing he saw were papers all over the floor. Upon further inspection, his eye sockets seemed to grow wider as he read over the papers upon papers of research.
Resets. Save points. Files. These words were only words he had seen in a video game once before. In reality? He had never expected to face a creature with such powers.
That's when it all started coming back to him. The good times, the bad times… all forgotten within the depths of the save files created by the creature that killed so, so many people.
He remembered them going through his puzzles that he had worked so hard on. He remembered when they had a date and he had to use the power of his "Cool Dude" outfit.
But most of all, he remembered getting to the surface. The surface, where all monsters dreamed of going to live peacefully with the humans.
And one particular human had taken that away from everyone.
Drip.
One tear after the other, they fell from his skull. He felt a fire burning within him. A fire blazing so hot, that it came to his skull.
He looked in the broken mirror on the wall, only to see a thousand replicas of himself with his right eye glowing orange. It then burst into a fire, and he felt his anger and hatred for the human.
He wanted to get revenge. They could have lived happily on the surface, with humans and monsters living together in harmony. Of course, it wouldn't be perfect. But he would be happy with all of his friends.
The fire blazed even brighter, until he felt everything around him go dark.
He felt a churning sensation, which would turn anyone else's stomach.
Suddenly, it got a lot warmer. He felt his surroundings change, but he didn't dare open his eyes.
"P-papyrus?"