- The premise of the book—that someone was able to make it so that absolutely no locks are functioning, including electronic and analog. You can't lock your doors, windows, computers, or anything. All of the basic safety measures we take for granted? Gone. The police end up having to investigate so many crimes that they're too swamped to solve the root problem in the first place. The entire town falls into chaos, and it's not even possible to leave because there's an invisible wall keeping everyone inside.
- The situation goes from bad to worse when Koudai discovers that it's progressing. Originally, it was just doors. Then guns stopped working because of the locking mechanisms inside. Then shortly after that, his car isn't working because he has to turn a key to get the engine running.
- The bear. Even before it starts hunting and eating people it's remarked on as much, much larger than most Asian black bears, and the horrifying illustrations of it in the book with its soulless white eyes doesn't help matters.
- The state that Shihogi Kanoe's body is in when Otoha stumbles on it in the music room, torn to pieces with her skeleton exposed. Just in case readers have any trouble visualizing it, there's an accompanying illustration.
- When the police finally locate Saruta Tsuyoshi the bear is eating his slashed up corpse. When they try to fire on it with tranquilizer darts, their guns won't work.
- Simply being trapped in the high school with it, none of the doors opening and having no possible way of managing the situation. Upon discovering this for the first time, after all of the desperate students and staff try every exit and find the doors stuck, the bear kills a teacher.
- When Otoha and Mizuki leave the relative safety of the band room to go to the bathroom, the bear ends up grabbing one of Seiryuu's friends. They can hear the sound of it eating him as they make their way back.
- As the bear eats more and more people, Otoha eventually thinks to herself that it doesn't look like a bear at all. It gets bigger and bigger and, among other things, starts emitting black smoke. The fact that it has the power to break locks and make invisible walls only compounds the question of what exactly is hunting them.
- While we don't know every detail yet, the idea of Allen Avadonia in some incarnation being the Big Bad is chilling to fans of mothy's prior works.
Nightmare Fuel / Unlock City