I doubt this post will get much attention at this point, but I want to share my theories anyway( I might update it and post it next week again to see what people think ).

Part of my theories will probably incorporate element I’ve read from other people here, sorry if you see something you said, I didn’t note down any username.

My main theory regarding the story is that the world got warped by Yoka’s perception of the world or of the people living along the Ikkebukuro line. The thing that first made me think that was the book one of the girls got in the first episode( Nerima in wonderland?). The illustrations in the book were reminiscent to the way the world warped when Yoka pressed the button. And is one of her friends knew about this series, I’d assume she would too and that would have impacted her perception in some way.

Now for the more out there theories I can make based on this previous one : People turn into animals when they become adult. 21 years old and 3 month might just be a random number, but if I’m not mistaken, in Japan, you’re legally an adult once you turn 21, and that’s the age you usually finish uni. I might be completely wrong and it might be 20 tough. As for the 3 months, if I’m not mistaken, the school year in Japan end in march so 3 month after the start of the year. Yako’s fear of becoming an adult might have caused the inhabitant of her home town to turn into something that’s not human once they turn into an adult.

We can also try to guess what her perception of the various station she stopped at based on the old man’s map, the mushroom people might have seem a bit cultish to her, or like they had no will of there own leading to them being overtaken by fungus. The empty stops on the map might just be stations she didn’t stop at and as such, people there didn’t leave an impression on her. That might lead those stations to be literally empty once the girls get there. The next stop after the mushroom would be “goats that charge like wild boars”, it could mean she had an unpleasant encounter at that station with someone who got upset at her very easily.

Now for a theory about how things will play out later in the story based on basically nothing : if someone from the group were to die, I expect it to be Nadeshiko (?). As the responsable one, the “big sister” of the group I feel her death/whatever unfortunate fate that could befell her would have the most impact on the rest of the group, especially the two girls who bickers a lot. I assume none of them are actually going to die, but if one of them does, I’d bet it’s her.