Well, the knockers did show up as a response to Fushi's existence altering the "natural order". In hindsight, Fushi could control the entire world if he merged with it. Every single living being would live at its mercy. No wonder they want him gone.
But is odd, the knockers got all killed before he went to hybernate. Does it take them a while to reform, and that's why they didn't show up when Fushi went to sleep? Because by the time they regenerated/made more knockers, there would be no active Fushi? Do they only move If he is active?
Hopefully we get more of Mizuha drama though.