An interesting take on Koishi's third eye. I've always read it as she herself closed herself off from the constant pressure of everyone having such hatred of her ability. In some cases tearing it off her actual body. Not born with it closed, forced open then sealing her powers herself.
When satori forced it open I felt really bad for her.
Also I had for some reason thought that the egg was going to be Okuu being born. but then you see her and Orin later