Eighth's diary is a server: anyone who runs a blog on it gets the effect. She sends some of her users to take out Amano.
The defense plan is: if they cut cell service to the area, Eighth's Child Diaries will stop working, and they can take them out.
But it's a fakeout.
The people who have actually come are not Child Diary users, but Seventh: Ai and Mar are lovers whose paired Love Diaries tell them how to protect each other. (They are both Seventh.)
They see this as a lover's duel: which couple's love is strongest?
It's Seventh.