This Gasai is an impostor.
Amano doesn't care.
--
Eleventh hooks up Eighth's diary to a supercomputer and gives everyone in the city an account: his plan is to be the leader of a clairvoyant kingdom.
Nishijima rescues Ninth from Eleventh's men and proposes to her!
Amano's friends team up with Ninth to take out Eleventh's supercomputers.
Eleventh's diary, The Watcher, shows him what everyone else's diaries say.
In fact, Eleventh was the one to suggest Future Dairies as a part of the death game in the first place.
Ninth figures it out.