This was really interesting. I'm always partial toward happy endings, but I try not to let my personal wishes for the outcome affect my opinion on the actual outcome. So, I will say it was pretty good. Had my eager to see what happens next from start to finish. Still wish it was a happy ending though.
I remember reading the first chapter of this a while back. It was really intriguing, so I'm glad it turned out to be a full series. Was it originally a one-shot, or was the rest of the series just ignored by translators for a long time?
I had guessed who the real Ouka was around halfway through. Regardless, it was a good twist. The series was excellently plotted and Sayman took the concept about as far as it could go without dragging it out. I actually feel like this was the most complete and coherent series I've read from them. It makes me all the more frustrated that so little of their work is published in English.
Getting personal, I also tend to use maladaptive daydreaming to cope with suicidal ideation (well, also out of sheer boredom). And, like Ouka's dreamscape, those fantasies aren't always filled with pretty, happy scenarios. The series takes a character who's willing to go to absolutely any length to be with the one she loves, and shows how that ideal can become extremely twisted and violent. Though the ending comes across as cynical at first, I think the overall point is how dangerous and pointless it is to retreat further and further into fantasies.
On a side note, it's a shot in the dark, but I'm guessing the CD/TG person is a representation of how Ouka views her actual body. She might be trans, or she might just feel insecure in her femininity.
Edit: Not sure how it didn't occur to me right away, but the final twist is basically the same as that of the movie I'm Thinking of Ending Things.