Well, I guess I'll throw in what I think.
Madotsuki could've seen Monoko's "accident" (Car accident?), and threw herself into denial, thinking she wasn't dead, but instead mutated. Monoe could've been a friend that moved away, causing her to "disappear" in her dream. Poniko could've easily been a side of her she didn't know about; a side that wanted attention. And Uboa could've been what she saw as "a creature lashing out" for the attention that Poniko did not receive.
I think the music teacher theory was a good one for Masada, but I think it represents a boy in her class, that was a mute, and very tall, causing him to be an outcast, which made Masada & Madotsuki friends, considering she MAKES herself an outcast.
As a child, Madotsuki could've been kidnapped, and almost raped- but the image of a man's penis scarred her, causing Kyu-Kyu to appear; and she probably feared sex, and pregnancy afterwards(The pregnant, headless "monsters" in her dreams.)
Or hey- to make it super simple, maybe she was a drug/drinking addict, and ended up in a coma, but when she jumped off her balcony(stress?) it signified she died in her coma.
Comment too long. Click here
to view the full text.