Thread:Isthereaplace/@comment-27907368-20160707013707/@comment-27620479-20160707162205

What I mean is, that the player is basically "fate", at least to a certain extent. Depending on their decisions and interpretation of certain game elements, the world of Undertale can be very different.

Not only in who you kill, spare, befriend, and flirt with, but also why, and then there is Chara's name and intention, Frisk and Chara's gender and background, what happens after the end, who is Sans, and what does the red soul color stand for, just to mention a few things open to interpretation.

The theory is that there is an Undertale multiverse, which encompasses the parallel universes of each copy of the game, and probably the fanfic AUs as well.