Yume Nikki Theory
1/25/13
Madotsuki: I believe she is a rape victim due to the fact that headless abominations with bloated abdomens occur on multiple occasions so she might have the fear of pregnancy due to the rape, and that there will be a miscarriage or deformities to the child before birth. Also in a certain area there is a zipper on the wall that you have to stab to open, which could possibly be a representation of the man unzipping his pants, further proof lies within the fact that when you step through the now bleeding hole in the wall you meet Kyuu-Kyuu kun; a phallus looking object rubbing a pole almost obsessively which could be a representation of touching before the rape. And when you enter the door in the area you are met with a ferocious and scary face, which could be the face of Madotsuki's assaulter. She could be dealing with a problem of self loathing or shame since she refuses to go outside of her apartment.
Or another possibility or side problem, she is dealing with survivor's guilt. Shitai could represent her mother and father's deaths due to a car accident and Monoe and Monoko could be her siblings that died along with her parents. This is backed up on the fact that Madotsuki doesn't look like she's even out of middle school and she's living alone with no supervision of any kind. She possibly doesn't go outside because people will pity her and she would start thinking about her parents and siblings deaths and hate herself even more.
Poniko: She could be Madotsuki's best friend in both scenarios above, but due to the fact that Madotsuki doesn't leave her house or go to school in either their friendship is dying due to Madotsuki's fears. The inability to interact with her could represent their distance in their lives and friendship.*
Masada: Masada doesn't exactly have to have been her teacher, but due to the fact of Sensei in his name it is widely believed that Masada was a music teacher at Madotsuki's old school and was a trusted adult, but due to the difficulty of reaching him in game, his and Madotsuki's relationship was also suffering from the rape or accident causing distance between the two.
The alarm that went off while crashing could mean someone called the police about Masada since they believed they were in a non-consensual relationship and that Masada was a pedophile that was assaulting Madotsuki sexually and they took him to prison. That could also form a distance problem since Masada wasn't allowed visitors or Madotsuki could go to the prison alone and she had no parents or her parents didn't know at the time.
Another could be that Masada was a drug addict and the crash symbolized his "crash" due to the drugs, which killed him.
Or that he was a person involved in the train accident and Mars san represents a person mourning the loss of Masada.