i was messing around in numbers world yesterday and thought about some things. i'm sure some other people have thought of these but here they are:
#1: numbers world represents fear of overpopulation.
madotsuki seems disconnected from society, obviously, so why wouldn't she be afraid of this? the long lines of deliriously smiling faces on the walls in numbers world reminds me of a stereotypical view of a crowd of people - all stupid and happy "herd animals". the numbers on the floor could easily be tied into the constantly exponential growth of humanity's population. the large area full of beds, too.
and of course, the stabbing room. it's impossible to navigate without killing the creatures, which is probably what madotsuki feels/felt like when she's been in a crowd trying to get somewhere. not to mention they're all blocking off a blue reservoir-looking thing. fear of losing vital resources, like fresh water, maybe?
#2: old ghosts from elementary years.
the whole layout reminds me of a school, seen through a very twisted eye. perhaps madotsuki had trouble learning the concept of numbers in itself, and felt like the overenthusiastic "happiness" of a typical classroom was mocking her. hence the strange wallpaper. there's also the stabbing room, again, which could be her "classmates", which the blue thing is the concept she's trying to understand.
just some thoughts.