You know, this brings up a problem I don't see mentioned: if Scarlet Star is a bunch of students passing on generation to generation for 500 years, how did nobody go, "Dope, this student constantly disappears whenever a void shows up!"
They may have been "dope a student disappears when a void shows up."
That doesn't mean they suspect suddenly that a 500 year old superhero, is actually a bunch of students taking turns passing the mantle.(in current case, a nobody loner). Far easier to believe the student is playing hooky, having a panic attack and running away, or a fan of Scarlett and wanting to get a glimpse of her, etc.
This isn't something like an iron man suit, where anyone could be inside. Who would genuinely expect someone to literally transform into another person entirely without seeing it happen.
And perhaps people did make the connection and figure things out. That one person helping mc leave, seems like they know something. There probably have been others who may have witnessed a transformation before
There also is the existence of magic, which commonly cognitively obstructs recognition in other magical girl series.
All in all most people are not both super observant(to routinely notice something) and open minded to unexpected ideas. It's super easy for us, because we are outside observers expecting this stuff.