I think that what they mean is that since the other paper demons were shown in the last novel (all sporting the Second Period names of the EC Demons of Sin), this novel might bring up the wrath paper demon. Who would, going by that standard, be Seth Twiright
The first chapter is from the perspective of Itsuki's mother, Kyouko. She talks with Masaki about everything in the previous novel (Haruto told her about it all, I believe). Masaki and Kyouko make some vague allusion to some ominous (group of people and the "witching hour"? I think this might be Evillious Net but it doesn't say) that they haven't told Itsuki about. Mostly recap it seems.
Second chapter is Itsuki finishing lunch at school. Haruto ropes him into playing his trading card game called "Master of the Demon" (which, incidentally, was made by the company Shigumi's father is the president of). The narrative explains that while Itsuki visits Haruto a lot, the secret library is always locked so he hasn't seen Marie in a while.
Third chapter is Itsuki and Haruto going to the school library. Shigumi is there. There's a Tsuruki City history book there, and a girl named Hadzuki (Hazuki) Mana reading a book called the "World Demon Encyclopedia". The history book confirms that the events of Unlock City happened twenty years ago. Itsuki recalls Marie telling him in the previous book how it had been roughly 20 years since she'd last gone out, so he decides to see if she knows anything about it (and also realizes that Masaki would have been in highschool at the time, and his mother in middle school).