@Shareazu—
Well, here are things bearing upon that question: [ul]The title is “
Shimeji Simulation”.
The world in which Shimeji moves has multiple oddities like one would find in virtual reality gone wrong.
The older sister seems to be wrestling with the structure as such of what seems to be reality.
The prequel involved the older sister beginning a project somehow associated with the suicide years ago of a girl whom she loved.
Chito and Yuuri make multiple appearances in this world, and Yuuri has alluded to
albeït in a way that Chito dismissed as hyperbole.
The apparent images of Shimeji and of Majime in
Girls' Last Tour are from the ostensible past of the world in which Chito and Yuuri live. [/ul] It seems that Shimeji is in a virtual reality. We don't know that anyone represented in this world has an existence outside of it. Chito and Yuuri could be represented in a single simulation during two intervals, one corresponding to
Shimeji Simulation and the other to
Girls' Last Tour. Or the world of
Girls' Last Tour may not have been a simulation, in which case the world of
Shimeji Simulation is likely to be a simulation within the world of
Girls' Last Tour.