Sayaka thinks she is mentally 27 years old, huh. I kinda wonder what a 27-year-old her would physically look like.
So it's not 1997 anymore, it's 2047. That's bonkers. If this isnt a true time leaping experience, there has to be an explanation why they keep their youth even after decades have passed. One way I could think of is that each time Akane dies, her memories are somehow transferred to a clone body who then wakes up and takes over as the experiment is restarted. The previous chapter already hinted at the possibility of clones with zombie Izumi and killer Izumi.
Just don't tell me the third party observer... is the real adult form of one of the girls. That's not it, right?
It's not often I encounter a manga where the main characters are living in what seems like an experimental playground being watched by outside administrators/observers. This is a mess, true, but at least it's not boring.