1. theory - Kyukyukun raped Madotsuki on her way home
Madotsuki has to enter him when she wants to go to her room/ her home.So I can speculate that Kyukyukun was a stalker or/ and a perverse. Maybe he allways waited at the same place for her. Of the movement of his armes i can image that he allways show Madotsuki some perserse things when she had to enter him on her way home. As a perverse her allways laughted and smiled at her and wanted her to go with him to his home and to rape her.
But whe he was only a perverse and not a stalker - he may met Madotsuki only randomly (A reason why you can find him randomly), took her at her hand and went with her to his home. They had to went upstairs and then he raped her - so I can explain why FACE was behind the door.
(BTW: Did you know that this sipper at the wall in the number world makes a greepy noise whene you interact with it? interisting, or?)
2.theory - the Birdhumans are her angry mother
When Madotsuki was hitten by them - she was allways in a small and unexcapeable room.
So I can image Birdhumans beeing her mother who was angry because Madotsuki did something very bad. Her mother may want her to be a good sweet little girl. Madotsuki tried, but she failed. Or the Birdhumans are angry because Madotsuki is outside and explore the surreal dreamworld. The Birdhumans wanted her to stay at home and not to see the world.The Birdhumans may have the helper syndrome or the maternity protection syndrome, so they only want to save and protect her. Madotsuki wants to see the world, but the Birdhumans send her into this small room, so she has to learn what she did wrong. The small room also can be a symbole for protection or isolation.
3.theory - Madotsuki saw "her stalker" in the mall and thought about the baby
In the Mall you can see at the wall some pictures (or posters) which show a person with something in his mouth (maybe a penis), a mouth with something flow out and at the lips (maybe sperm) and a poster with a fetus or a embryo.
I can image that her might saw the person who rapped her. Whene she saw him, she remindes the bad and aweful things he did with her. Maybe she thought at the same moment about her baby (from him).
I also can image that she abort it in the room with the thing at the blood pond. Maybe the baby was a miscarriage or/and premature birth so she lost much blood (so might arised the blood pond). So I can conlcude that the greepy thing may is a symbol for her vagnia, because blood came out it when the baby was miscarriage (the poster at the wall) the blood didn´t get lost and was collected in the pond.
(well...because a good tip of a user I remade ^^)