pkay so n bad at explaining but uh
i have a feeling the main protag u start with in DF (idk their name) is sort of like an "anomaly" that was there in the timeline for a while, (perhaps a gaster experiment?) but uh, the appearance of the anomaly caused stuff to mess up and they had to move (abandoning the past locations, hence making lost worlds) and some people (toriel, undyne, and other people missing in game) and got corrupted by it and sm enemies did too (the MissingNo, beta enimies, bugged enimies etc) and MC does know what's going on, knows they're not supposed to be there but won't (defying fate) an gaster is trying to bring everyone back with scienxe stuff but he got corrupted in the process
i think??