Nodoka knows too much. According to her, she was not born human. Maybe Nodoka is the narrator. Not Himawari.
I do wonder if Nodoka's presumed relative Kyoko, is involved in some way as a Narrator or something.
From what I remember, there are about 3 to 4 narrators, so maybe I just don't remember exactly who the 4 are.
There definitely seems to be more than one. Plant #2 claimed so:
I think Sekai is the one that talks about the gods, the Shapeshifter/Himawari is usually the one at the beach, then there's Sensei, and apparently something that thinks they are Sensei.
There might be some others though, like the one that seems to hate Sensei, albeit they may actually just be something with a split personality, or something.
about upside down house: im now replaying game , and i am baffled by how many times i didnt notice anything strange on TV, do we have any good theories what the hell is it?
It seems like the Upside Down House is some kind of other world that is layered on top of this one. Kumon-mi seems to be World/Terminal 23:
So, the UDH might be 24, since 22 is gone. Unless the UDH is gone and we've merely been experiencing remnants of it, making it 22.
There's presumably older relatives of the Arakawas (Ami and Sensei), and Nagasawas (Nodoka), in the Upside Down House, so I guess it'd make more sense for it to be an older world.
Overall: It's not exactly clear what it is or why it exists.