It's honestly hilarious that Chika and Yumi basically talk about Sensei all the time and they don't even know his name. Like, has it even been brought over the several resets that Maya witnessed before?
As we learned lately people were calling Sensei Akira all the time, at least if they knew that name.
That's were the term perception kicks in again.
From Akiras point of view/perception all the time he was called Akira, he percieved it as Sensei.
This raises another question.
Now that we're told "this is not a simulation" blah blah (cmon really?) that could mean every single person in Kumonmi could misperceive alot of things, like Akira with his name.
Like, everytime we have a user x logging in, might be that the person in the current scene is, in reallity, talking with someone thats invisible for them, or looks like just some passerby.
This could in return mean that "the gods" or whover is responsible for the resets/cycles and whatnot, might be walking around in Kumonmi without anyone sensing something special about them.
Could even mean that Sekai was never dead to begin with, she was just faded out from everyones perception, till what ever happened (maybe by her own will) made her visible again.