At "Day Five", you have to choose your way. When Shinji come in, he will talk to you, you may make decision, is it a delusion, or it is a real? That is barrier between Good and Bad ending.
If you choose '"'There's Really A Monster" and go to the study, you will meet the monster. After that, you will run to the basement. The monster will meet you there and gives you a teddy bear with Miki's name on it (protagonist). Miki will reminisce about her Aunt and finally realized that the monster was actually Saeki. You will be woken up by Miura, and will be told that an ambulance is coming for her, as she fainted and didn't wake up when he shook her. After that, the monster no longer chases her from then on. At the end, she is leaving the house to go back to her mother, as her mother's hysteria has gotten worse. Miki is diagnosed with schizophrenia, a condition where an individual is unable to tell apart reality from fantasy. She mentions she will go back to live in the house again when her condition is better.
If you choose "It's Just A Delusion" and go to the Study. Miki will say that, it is her fault as she says "I killed my aunt". Then we can see "THIS IS FANTASY" and "THIS IS NOT REAL" screen. Miki will refuse to hide from the monster, thus she is killed by it. Last thing we can see are newspapers where is written "Girl was found dead". It is unknown if Shinji Miura believes the monster at that point after finding Miki dead in her own house, even though Miki confirmed to him previous that the monster "might" be a delusion.