I was sitting on Nico Nico the other day, watching Yume Nikki, and then this crazy (or not so crazy) theory popped in my head.
So like, Poniko, Monoko, Monoe and Madotsuki, were all friends, and they were having a great time and stuff. Then some creepy drug dealer was like, trying to make them try drugs and Poniko, Monoko and Monoe decided to take them.
Madotsuki was a good girl, and didn't take them, but they tried to make her take them. Monoko though was trippin out and stuff though, so she got hit by a car, and Monoe blamed it on Madotsuki (for whatever reason) and now always just smiles and walks away from Madotsuki from that day. (explaining what happens if you interact with Monoe.) Poniko though would not back down, she would always try and lure her in with that smiling face, but beneath it would be Uboa. So Madotsuki locked her self in her room from the pressure, and whenever she would gather the courage to open up the door, she would just back down again.
Soon, all of this stress went into her dreams. Dreaming about all the pain and terror from her friends, until she snapped and committed suicide.
So, what do you think? Sorry if this has been thought of before, but this was in my head, and I had to write it down.