Undertale: An Unexpected Story

What kind of story would unfold if everything had already changed from the very beginning, yet somehow it remained just as it was before? Some things that should have happened never did, while other things that should never have appeared did. Everything is full of contradictions, and yet it all makes sense.

Note: The above is pure nonsense. This is an Undertale fanfic. Before reading, please make sure you've played the original game and Deltarune, and have some familiarity with the fan community.