That seems like a very specific thing that I don't recall happening anywhere in the previous chapters, and doesn't seem connected to modifying humanity's mantra to save her.
Not explicitly stated but it is explained bit by bit from the very beginning. Especially when the kami talks. Btw Hitokotonushi future is death, he is killed by Ozuno, then he go back to the past, become a bit crazy, and become his own past self master (heavily hinted), but... In the very first chapter we see older Miyo met older Ozuno and Zenki and both of them look very healthy.
as always, this story gives us a weird but tasty bland of mythology and sci-fi.
