Responses
Didn't the lore of this story already mentioned that there came a time when an otherwordly being came to Earth. The humans weren't capable of beating down that being. However, that being "enveloped/embraced" humanity instead of destroying it. Most of the humanity venerated this being in the end, enabling other beings to reside the planet. For me, that's clearly what was depicted in the mural.
Oooh okay, ig it just felt sinister to me? The remains we're all posed like they were in the middle of worship as they died so it seemed off to me.
The mural depicts some kind of alien, hugging an entire community of humans. The alien was drawn as a CIRCLE with all the humans inside that circle. Also, there's another detail of human remains worshipping the mural.
Could it be that Mori was somehow a part of that (possibly abusive?) community which is why he has a trauma of circular light/thingies? Although it could be very possible also that it's just a coincidence.