Good point. Now that that's out of the way, I was also having a conversation on what the final boss's ability might be with a few friends.
The final boss's ability might be something like, 'The ability to animate objects', and the stage 5 boss has 'Manipulation of Will'.
Manipulation of Desire wouldn't work, as Miko already can hear desires, but if someone controls your will, you have no control anymore. It would explain why all the youkai want to be exterminated by the crazy shrine maiden, because they're not in control of themselves.
I'm also going to say it here, there's a high chance Mamizou will be a midboss. After all, the title of her stage is 'Raise the Flag of Rebellion', and ZUN even said that the title would tie into the next game. There's a good chance she's partially responsible for something.