Wait where did geto is kamo come from?
It's mainly just a theory. The fact that Kamo is referred to as the most evil sorcerer in history will definitely come into play sooner or later.
It's also quite interesting that when we got his pic we can't see his forehead, it's covered in shadows. It probably has stitches too.
It's more than likely he had stitches too and Gege hid it to not be obvious. It could also mean the brain actually inhabited him too and is some older entity and not Noritoshi. Also you can see he lived around the Edo and Meiji era. In the beginning of meiji era is written above, and Meiji era came right after Edo era. Noritoshi probably lived through the end of the Edo era and the start of the Meiji era. Geto in the last chapter starts talking about the Edo era.
Also Choso and his brothers are the curse wombs Noritoshi was working on with the woman above. And now they sided with Geto.