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.
Seventh take Amano and Gasai's diaries and send everyone to the hospital.
Ninth arrives to train Amano for a plan to beat Seventh. This is fake, but if Amano believes it, Seventh will read it in his diary and be fooled.
Amano's father arrives. He has been suborned by Eleventh.