I still firmly believe Mizu isn't the main culprit and not Karasuma's primary target. My working theory is she's another victim of whatever killed Aizawa. There's a lot of exorcist detail that doesn't tie into the idols: Karasuma's passivity, Michi's mom, Sayaka's bloodline. And you can't have a Japanese ghost story without a dangerous mountain spirit. But then the question is how it became entangled with De:Lphinus in the first place, what Mizu's goal is, and how Michi is going to get to the bottom of it all.