So this is my theory...
In end there is a special scene where the headlines and picture of the murder of the red person changes intlo asuka's.

So from my point of view i think that asuka is actually murdered when she was 8 and in the whole movie asuka's character is just hallucination .

In the scene where they are in the library and Takahiro say something about him going to amusement park with asuka's family but she cuts off in the middle and in the ending scene they showed that she was murdered in an amusement park.

Next when they went to beach Asuka says that when they were younger they had a school trip like some swimming trip or something and she did not attend due to her cold but on next day they all saw her as invisible and forgotten I guess that's when she was murdered because of that they did not actually saw her and even she didn't know that she actually died.


I think they saw her at night because she only appeared to everyone at night for body search because she is the next person for body search. And Takahiro is the closest person to Asuka that's why only he saw her even at morning.


* THIS IS ONLY WHAT I OPINION AFTER WATCHING IT *