Release That Witch - Chapter 53 Holy Mountain

Maybe all me theories about the monsters were wrong. To me, that looked like a hyper-futuristic city, and I doubt it was an illusion. It’s either in an autonomous state, or people/a race uses it. An autonomous state would make more sense, especially if the monsters come from there. If it moves around, that would explain why demonic beasts show up at the same time each year.

I also think it may have been where the witches originated from, due to humans experiments. It would make sense if it’s a lost relic from a very advanced civilisation, almost like the floating castle from Castle in the Sky, with all the ancient technology. That was automated, and hyper-advanced, but no living being lived there.

I’ve had many theories in my head up until now, but after seeing that, I am pretty sure that’s the source of monsters and witches. They also acknowledged it as a city in the text and stopped calling it a mountain when they saw it, which means the author is basically saying it’s a city.

However, the protag did come from another world, so rather than it being autonomous, maybe it briefly appeared from a different time/place? Hard to say, but imo, it at least covers the mystery with where all the non-Earthly phenomena comes from.