So yeah simulation confirmed.
Yet I have a theory big sis created the simulation. There is not many people in west yomogy. They lost their parents (probably in GLS war). It was a chance for her little sister to have a normal life. The egg and the shimeji was but bugs in the simulation. The angels probably were co scientists , but everyone lost their memories before going into the simulation and only had a somewhat % of it. But we need to be careful cuz this can try to get out of the scope of the direction of the desired narrative.