So wait, then the OG Ouka was the idol in the third chapter all along? Because the dude in the train called her the same as the idol and they look similar...
Now I also think that the trans person is just another version of Chihaya that exists in Oukas mind. That's why they can also travel between levels (I think that was already theorized before)
Last chapter felt kinda rushed, but oh well
I think too the characters got what they wanted in the end, even though it's still a twisted end.