THEORY NUMBUH ONE:
Madotsuki worked at or frequently visited a store that sold Music-related and Videogame-related items, the Catface coin was the store sign/logo, the Cat effect it gave and what it does may be a reference to there being a "Money Cat" in the store, or Madotsuki was working as the mascot and had to wear that as a costume. Seccom was another guy who worked in the store or frequented it(and was obviously a pianist or keyboardist or worked in the part of the store carrying them, and note how he makes a sound from Mario World). Neon World was an old Arcade game Madotsuki saw in the store, the Famicom worlds were a videogame Madotsuki was fascinated with, the Bicycle is how she got to the store, the flute was an instrument she could play, the Aztec imagery and Kalimba music suggest a fascination with world music, the rave monkey and the Toriningen party music representing other genres of music she liked or heard in the store. The Block world is a blurred memory of the city district the store was in, and Eyeball world was this feeling she could never shake off that she was being watched as she rode past this bad or creepy area, the Mall could be a place the store was in, Number world's round inhabitants with legs and the dude who gives you the flute effect represent CDs. The dude who gives Mado the flute could also have been a muse or something, and the place where you find him was a fertility clinic in the mall (note the condom poster and the egg-and-sperm poster inside it).
THEORY NUMBUH TWO:
FACE is Azathoth and Kyuu-Kyuu's rubbing constantly keeps him asleep and stops him from destroying the dream world, which is why he never stops rubbing and can barely be interacted with, and why FACE is so goddam disturbing.
THEORY NUMBUH THREE:
Kyuu-Kyuu was a weird guy who liked Mado IRL and hanged out near a staircase a lot and tried to get her attention. FACE is what happened when Mado ignored him or hurt him one too many times and he goes INSANE at her.