A human in your AU's timeline had started a genocide, killing anyone they met. Eventually, they gained enough power to erase the tinelime completely. But before they did, Core!Frisk (or just Frisk) crawled out of a trashcan in front of you

"Hey, I know a safe place!"

They explained that they had a place where you would be safe frlm the erasure, after accepting, they then told you the instructions on how to enter the Omega Timeline, so you thought of the Omega Timeline, opened a door and walked inside, and boom, you walk into a white void, with a town in the distance that has a blue sky around it. You see Frisk in front of you waving

"Hello, Welcome to the Omega Timeline, you can call me Frisk." The monochrome child said "You can stay here for as long as you like!"