I think this is what I'm taking issue with. I think that due to the supernatural forces at place, everyone's subjective experience is becoming equally real. In a world defined by perception, what would just be a hallucination in our world is just as real as what Maya is seeing at the same time. I don't think there's a "real" way things actually are below the subjective level, the platonic truth has been cut out from under kumon-mi and now it exists as a reality made of shared experiences.
Setting aside my suspicions about barb and the other weird object people (They're literal pareidolia...) , if she wasn't real on her own, I think to some degree Sensei sort of made her real. Maybe not an independent consciousness but his funky perception made a collection of objects start acting out a character.
Granted, I'll admit I'm kinda swinging wildly for the fences and could be totally off base, but I think that's the most fun way to interpret stories before you know all the details. And hey, I guessed out like 90% the plot of Armored Core 6 (mostly about the true nature of coral and the existence of C-machines and such) and people dismissed my ideas back then, so I've been riding that high ever since.
Speaking of Barbara, this has been bugging me for a while. What is her mouth? Is it just a mouth? When I don't look at it dead on it looks like it might be made of other stuff like her facial features but looking closely it just kinda looks like a mouth.
I think the main difference between our theories is that you're working off the theory that this world is defined by the perception of others. While I'm working off the theory that the perception of others is defined by this world. The various Mayas, Amis, and well everything, only mean something because we are aware of the characters themselves. The World that Sensei knows, defines his Perception of this World. It doesn't actually change what he's done, how the world works, or why it works that way, but he likes to pretend it does.
It's why we and Sensei apparently didn't hear or see his name, even though Noriko and seemingly others have been calling him Akira this whole time:
It's probably why even Yasu has explained that Sensei only thinks she's doing things:
Basically everything in the 'Mother's Milk' Happy Event is about Perception merely being shown to be Perception, and nothing more.
Even the game doesn't really care about our Perception of things. It'll shut off if we don't do what it wants us to. Choice is merely an illusion, and even the latest update showed that whether you're on the "good uncle" or "bad uncle" route, it doesn't
really matter. You are still following the script no matter how you perceive the script.
Overall: I consider everyone's subjective experiences as merely subjective experiences. What's "real" is what can't merely be considered a subjective experience for one person.
For example, the Upside Down House and what's related to it, isn't like Barbara which only Sensei has seen and killed in a Reset. Nodoka has apparently drawn the house, Futaba has found and read a notebook related to those in the house, Otoha has seen it on her TV, Noriko, Kirin, and Niki, have apparently watched those within the house eating. Etc.
Then there's Nao-chan who many people have seen, and even though she seems like she'd be a hallucination, she's apparently "real".
To sum it up, I don't think it's "real" that Sensei is pregnant with Haruka's child:
Even though that was a subjective experience by Sensei and us. Some things are just hallucinations.