Just a little mix between HorrorTale and Story Shift. I don't know if this is already a story or not, but here it goes.
It's been many years since the human fell down. The 6 souls disappeared and the King was dead. Since there was now next to no hope for monsters reaching the surface, the Underground fell into ruins. Monsters turning against each other and and under Queen Toriels command, any human to fall down would be brought to her for execution.
Frisk, now 14, knew what they did. They didn't try to help the monsters in the underground and thanks to them, Chara, the other human in the underground, would be hated. Everyday they'd have nightmares about the ordeal. They knew Papyrus, caretaker of the ruins, would go insane from the lack of people to talk to. They knew Asriel, child of Toriel, would be trying hard to join the royal guard, maybe even turning against Chara, his sister. They knew that Asgore, the royal scientist, would eventually leave his family behind. They knew that Blooky, Mettaton, and every other monster in the underground would perish.
Frisk wants to help. But will going back into the underground help? Probably not. But they are filled with DETERMINATION