After that episode where we saw how Menou became a priestess, I came up with the theory that after a certain point, a sizable amount (if not all) of the priestess could in fact be otherworlders.
The last few episodes tells me that Akari didn’t have a fun life in Japan (At least with how much she can remember), and somehow form a bond with Menou that I guess when she learned she needed to be killed, she would rather have it be by a good friend, and not some rando or someone she hates
Flare knowing about the time warping is most likely tied to my theory about priestess being otherworlders after a certain point, and Flare might be close to being one of the sins like Pandæmonium
I think it’s possible that Manon could have a pure concept, but the world doesn’t know because most otherworlders are killed off before they have offspring, and most that do, their children don’t have it, so at some point, they just assume otherworlders offspring won’t have pure concepts. But if the mother was pregnant when summoned, that might be why no one questioned the first child born from an otherworlder had a pure concept and they assumed the other didn’t.