Taking place after the end of the Pacifist route, Frisk has worked hard, with the help of her friends to secure the integration of monsters and humans. The Seven years of political negotiations have secured homes, jobs and economic stability for the newcomers into the human world. Monster councils and task forces have been formed and all her companions have specific and important duties to perform. And Frisk, Ambassador and new graduate, is ready to enter the work force and become an adult. Everything seems to be perfect.
That is until Alphys, experimenting with the alternate timeline theory uncovers something dark and, even worse, may have brought it into their own timeline. With this newfound challenge, Frisk must battle a new monster, one that can't simply be spared or killed. Will Frisk's determination be enough, or will she bring about the destruction she has sought her whole life to avoid?