tsuchigomori
I think they prevented the impostor Tsukasa to come to the human world in some way, maybe be sealing the god or killing the impostor. The real Tsukasa sacrificed himself so that Amane would get better and could become an adult. This Tsukasa then turned into the boy with a hole I guess? But they must have changed something after the sacrifice.
There was never really an impostor tho. Like, we saw Tsukasa throwing himself to save Hanako, and then in the red house he decided to come back. The Tsukasa from the red house is the same child we saw sacrificing himself, just like the kannagi used to do. He came back with the god attached to him, I guess, but I dont think there was ever an impostor. In the end, we still don't know what they changed tho. Not sure if even Time has the power to seal a god.
It /is/ Tsukasa, in some shape, given the little moment when he called "Amane", but we dont really know what they changed................ Like to get this timeline, they either had to kill Tsukasa before he reached out to the god, or seal the god, but not sure if they can do that?????? Also, where the hell is spider sensei (his name is too long to remember sorry) and why would this mitsuba remember being a supernatural, when the mitsuba who was a supernatural was something tsukasa created?