The students are all Remnants of despair or something similar, and Kyo at least partially remembers.
To expand on this... it's possible that Kyo has resistance to toxins due to his talent, and that he resisted whatever drugs were used to erase the other students' memories. His wild-card behavior is based on knowledge he has which the other students have forgotten. Mamori is the culprit of chapter 3.
- note how he was acting awfully suspicious after discovering the second body, talking about giving his life—and how the first body didn’t cause an announcement despite three people being there. Since the killer doesn’t count to that total and Hanase wasn’t involved, that leaves Chie and Mamori as the biggest suspects.
- Jossed.
Delilah is actually Aisa in disguise.
Aisa is amongst the missing students, and suddenly there's this new student that appeared out of nowhere. It's entirely possible that Aisa could have used her skills as Ultimate Make-Up Artist and the prosthetics in her room to disguise herself as a new student.I'd guess that either she's the culprit trying a novel way of escaping punishment, or she's hiding from the killer, or those who suspect her of being a stalker.
- Another possibility is that she’s protecting the missing students somehow.
- Seemingly jossed as of the Chapter 3 trial, but... It's still a possibility. The only ones to confirm Aisa's death were Delilah, and the killer themselves. If Aisa is disguised as Delilah, there's a strong possibility that she's the other werewolf. And with how well Oboro was able to disguise as Seisuke with the makeup kit...
Chapter 3's trial ends in graduation.
This is the reason why the following chapters are considered 'Season 2'. The surviving students get the killer wrong and get executed. However, it turns out the students who disappeared actually escaped, and the story continues with Kouki as the new main character (which is the reason for his ahoge).- Jossed.
Alternatively, the missing students will bust into the trial in a Big Damn Heroes moment.
Why? Because it would be cool. Before the killing game, Mamori was working for one of the Werewolves.
There are two ways this theory could work. Mamori’s memory of working with the Werewolves were wiped out. Or the Werewolves he was working for are hiding their identity/true appearance. In the prologue, Mamori states he “cannot find his most recent client.”*assuming he isn’t lying. Mamori did not react or mention his recent client when talking with the rest of the cast. Thus, in order for this second reason to be true, the Werewolves have to be using a disguise.