Samuel creates a beacon to attract all the Flame Hazes, but the Denizens try to hold back their attack, believing it to be an obvious decoy. Shana and Wilhelmina keep up the act by fighting Sydonay and making him believe they are trying to protect something. Centerhill and Margery then arrive, and once the Flame Haze evacuation is complete, Centerhill stays behind to sacrifice himself, allowing Shana, Wilhelmina, and Margery to escape.
So Centerhill appears to give us the beginnings of an explanation of why Yuji and the Snake’s plan is bad: apparently the consumption of Power of Existence by Denizens create disturbances which collect in the void, causing the storms and disruptions there. If the Snake creates a new world there, where Denizens can consume unlimited supplies of Power of Existence, those disturbances will rebound back onto the real world, having nowhere else to go, creating a disaster.
This, of course, would result in the destruction of the world, not the saving of us, as Yuji wishes. Whether this is the Snake’s true intention, which he is hiding from Yuji, or whether he truly believes he has somehow bypassed this problem, I don’t really know. Clearly Yuji believes he has solved this problem (or isn’t aware of it in the first place). In any case, it’s clear why this solution isn’t preferable to the Flame Hazes.
So it looks like Shana’s next goal is to meet up with the remaining three Gods of Earth and to convince them to join the Flame Haze’s fight. Centerhill didn’t seem to particularly powerful, though I don’t know if that’s because he held back, or if they use their power in a different way (in Centerhill’s case, in order to make it rain and to grow trees) I don’t know. In any case, I’m sure having the Gods of Earth can’t hurt their cause.