Since we don't have the full text, it's hard to say precisely. However, generally, the plot could start with Monika realizing that her world is a fan - made game story. Then she might try to communicate this to other characters. There could be conflict if some characters don't believe her or if there are rules within the fanfiction's game world that prevent her from spreading this knowledge. Maybe she has to find a way to prove it, like showing glitches or inconsistencies that only make sense if they are in a fictional game world. As the story progresses, the reactions of the other characters and how they deal with this new - found knowledge could form the main part of the plot.
I'm not sure of the exact plot without more details. But it might revolve around Monika making others aware that they are part of a game - based fanfiction.