Story analysis: my take! Spoilers.
I love this film so much, and I think me and my sister have figured out the story..
Mima is a pop idol. She leaves the business to become an actress, because she wants to, her reps want her to, and she believes the pop idol business is going downhill.
She takes the role of the MPD character on Double bind. Her mental health slowly disintegrates when she learns of the website, Mima's room. She doesn't use the internet, so she thought it was someone actually watching her real room.
In reality, her rep, Rumi, is obsessed with her and flipped out, as she wants Mima to be a pop idol, and she ends up believing she is Mima, and she's the one behind the website.
Mr Me-Mania is the second biggest fan of Mima, and Rumi tells him in e-mails, that the real Mima is an imposter and SHE is the real one, without saying she's in-fact, Rumi.(Rumi is Mima's biggest fan, and Mr Me-Mania believes that online-Mima, is Mima.)
Mima ends up becoming her MPD Double Bind character, but the only person she kills is her photographer, as she couldn't stand the degradation. Mr Me-Mania kills everyone except the photographer, and when Rumi tries to finish the job when Mr Me-Mania is killed by Mima.
So in the end, Mima and Rumi are both mentally ill, but with different outcomes. Mima has become the new Mima, has let go of the past, but for a time believed she was the character in Double Bind. Rumi is stuck in the past, from being the biggest Cham fan, she wanted to become her when Mima left Cham. This went to the point where she saw her own reflections as Mima, while the real Mima just saw hallucinations of her original self, as everyone was pressuring her to be an actress or an idol.
-] Horror Fantatic [-
"She lives in the tongue, Sir. You know that."
"The Beast watches."