The birds was singing, the flowers were blooming, it was really a beautiful day outside, or it had been, but wasn't anymore. Except the birds, not a single living thing in sight, and there was no other sounds either. The towns were completely empty, it was like the whole world was screaming in fear. You could smell it in the air, something was terribly wrong, and they knew why. It was because of them. It was their fault that the whole Underground was filled with fear, and they loved every second of it. Tracking down innocent monsters, that has been hiding from them, and that shaked and screamed and pleaded as their lives ended, and they turned into dust. They loved to see the monsters last second of life, the moment of absolute fear before the kill. Their hands always getting dusty after every kill, and how they just left the monster dust were it was, so that they would never get a proper burial, so that their essence could never live on in their favorite things, since the filthy monsters never deserved that since they never wanted to help them to get back to the surface, because they didn't want them to "kill a monster just for going across the barrier since that is unfriendly". This was their revenge on the monsters, since they never wanted to help them, since they thought killing once monster was unforgivable, they would kill everyone they saw just to make the monsters suffer even more, so that they would see their mistake for not letting them leave all those years ago. They were gonna make the monsters lives a hell over and over again, and they would do it with a smile. A smile that existed because they knew how much stronger they were, even in this weak human body, they could easily kill all of the monsters. They were practically the God of those monsters, the God of death, and they wanted to keep it that way. Destroying the souls of the innocent.
For them this was just a game, a very funny and entertaining game. Killing their once so called friends over and over again, and erasing the world over and over. And they kept resetting the world to find and even more gruesome way to kill all of the monsters every single time. They were no longer a kind innocent human, they would never even consider doing a pacifist run once more, they would just get bored of those useless monsters. Killing everything was much funnier, and it gave them more power, and lvl. Every time they killed a monster, and their lvl became higher, they felt more alive. More Godlike, more mighty and more evil, the best feeling they had ever felt in their entire life, both their own and in the life of the human that they possesed. They swore that they would never stop doing this, they would continue in this time loop forever. Killing everything and erasing the world over and over again, until they got bored and would do a last pacifist run so that they could then kill everything in the human world too. They were looking forward to it, the day were humanity would get to pay, and that people would realize that the only monster down here, was them.
Them as in Chara, since Frisk was dead a long time ago, and had to fight to get into control but always failed. Feeling Frisk cry while they killed all the people they cared about made everything funnier. Their mom, their dad, the skeletons, the fish, the lizards, all of the citizens. They could feel Frisk cry every time they got killed, and that filled them with more determination. Determination to kill and make their life a hell.
They never want to stop.